From 0e81d71fbbb146ee448594e3dcdf9b45b4acdf2a Mon Sep 17 00:00:00 2001
From: Jon Sequeira <jonsequeira@gmail.com>
Date: Sat, 12 Mar 2022 11:28:09 -0800
Subject: [PATCH 01/11] wip

---
 .../CommandLine/Perf_Parser_ParseResult.cs    |  2 +-
 .../CommandLine/Perf_Parser_TypoCorrection.cs |  2 +-
 .../ParameterBindingTests.cs                  |  2 +-
 .../CompletionContextTests.cs                 | 20 ++++----
 .../DirectiveTests.cs                         | 20 ++++----
 src/System.CommandLine.Tests/ParserTests.cs   | 51 +++++++++----------
 src/System.CommandLine/Option.cs              |  4 ++
 7 files changed, 51 insertions(+), 50 deletions(-)

diff --git a/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_ParseResult.cs b/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_ParseResult.cs
index f3ca5fcc65..bf48c05412 100644
--- a/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_ParseResult.cs
+++ b/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_ParseResult.cs
@@ -20,7 +20,7 @@ public class Perf_Parser_ParseResult
 
         public Perf_Parser_ParseResult()
         {
-            var option = new Option("-opt");
+            var option = new Option<bool>("-opt");
 
             _testParser =
                 new CommandLineBuilder(new RootCommand { option })
diff --git a/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_TypoCorrection.cs b/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_TypoCorrection.cs
index 6532821c1f..63a4996c95 100644
--- a/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_TypoCorrection.cs
+++ b/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_TypoCorrection.cs
@@ -22,7 +22,7 @@ public class Perf_Parser_TypoCorrection
 
         public Perf_Parser_TypoCorrection()
         {
-            var option = new Option("--0123456789");
+            var option = new Option<bool>("--0123456789");
 
             _testParser = new CommandLineBuilder(new RootCommand { option })
                           .UseTypoCorrections()
diff --git a/src/System.CommandLine.NamingConventionBinder.Tests/ParameterBindingTests.cs b/src/System.CommandLine.NamingConventionBinder.Tests/ParameterBindingTests.cs
index 2f0530845b..74b7ecedbc 100644
--- a/src/System.CommandLine.NamingConventionBinder.Tests/ParameterBindingTests.cs
+++ b/src/System.CommandLine.NamingConventionBinder.Tests/ParameterBindingTests.cs
@@ -51,7 +51,7 @@ void Execute(string firstName)
 
         var command = new Command("command")
         {
-            new Option("--first-name", arity: ArgumentArity.ExactlyOne)
+            new Option<string>("--first-name")
         };
         command.Handler = CommandHandler.Create<string>(Execute);
 
diff --git a/src/System.CommandLine.Tests/CompletionContextTests.cs b/src/System.CommandLine.Tests/CompletionContextTests.cs
index 507dd38545..d1a371368c 100644
--- a/src/System.CommandLine.Tests/CompletionContextTests.cs
+++ b/src/System.CommandLine.Tests/CompletionContextTests.cs
@@ -76,8 +76,8 @@ public void When_position_is_unspecified_in_string_command_line_not_ending_with_
         {
             var command = new Command("the-command")
             {
-                new Option("--option1"),
-                new Option("--option2")
+                new Option<string>("--option1"),
+                new Option<string>("--option2")
             };
 
             string textToMatch = command.Parse("the-command t")
@@ -92,8 +92,8 @@ public void When_position_is_unspecified_in_string_command_line_ending_with_a_sp
         {
             var command = new Command("the-command")
             {
-                new Option("--option1"),
-                new Option("--option2")
+                new Option<string>("--option1"),
+                new Option<string>("--option2")
             };
 
             var commandLine = "the-command t";
@@ -130,8 +130,8 @@ public void When_position_is_unspecified_in_array_command_line_and_final_token_i
         {
             var command = new Command("the-command")
             {
-                new Option("--option1"),
-                new Option("--option2")
+                new Option<string>("--option1"),
+                new Option<string>("--option2")
             };
 
             string textToMatch = command.Parse("the-command", "opt")
@@ -146,8 +146,8 @@ public void When_position_is_unspecified_in_array_command_line_and_final_token_m
         {
             var command = new Command("the-command")
             {
-                new Option("--option1"),
-                new Option("--option2")
+                new Option<string>("--option1"),
+                new Option<string>("--option2")
             };
 
             string textToMatch = command.Parse(new[] { "the-command" })
@@ -162,8 +162,8 @@ public void When_position_is_unspecified_in_array_command_line_and_final_token_m
         {
             var command = new Command("the-command")
             {
-                new Option("--option1"),
-                new Option("--option2")
+                new Option<string>("--option1"),
+                new Option<string>("--option2")
             };
 
             string textToMatch = command.Parse("the-command", "--option1")
diff --git a/src/System.CommandLine.Tests/DirectiveTests.cs b/src/System.CommandLine.Tests/DirectiveTests.cs
index 37ea2573d5..9bddbe564b 100644
--- a/src/System.CommandLine.Tests/DirectiveTests.cs
+++ b/src/System.CommandLine.Tests/DirectiveTests.cs
@@ -14,7 +14,7 @@ public class DirectiveTests
         [Fact]
         public void Directives_should_not_be_considered_as_unmatched_tokens()
         {
-            var option = new Option("-y");
+            var option = new Option<bool>("-y");
 
             var result = option.Parse($"{RootCommand.ExecutableName} [parse] -y");
 
@@ -24,7 +24,7 @@ public void Directives_should_not_be_considered_as_unmatched_tokens()
         [Fact]
         public void Raw_tokens_still_hold_directives()
         {
-            var option = new Option("-y");
+            var option = new Option<bool>("-y");
 
             var result = option.Parse("[parse] -y");
 
@@ -35,7 +35,7 @@ public void Raw_tokens_still_hold_directives()
         [Fact]
         public void Directives_should_parse_into_the_directives_collection()
         {
-            var option = new Option("-y");
+            var option = new Option<bool>("-y");
 
             var result = option.Parse("[parse] -y");
 
@@ -45,7 +45,7 @@ public void Directives_should_parse_into_the_directives_collection()
         [Fact]
         public void Multiple_directives_are_allowed()
         {
-            var option = new Option("-y");
+            var option = new Option<bool>("-y");
 
             var result = option.Parse("[parse] [suggest] -y");
 
@@ -56,7 +56,7 @@ public void Multiple_directives_are_allowed()
         [Fact]
         public void Directives_must_be_the_first_argument()
         {
-            var option = new Option("-y");
+            var option = new Option<bool>("-y");
 
             var result = option.Parse("-y [suggest]");
 
@@ -72,7 +72,7 @@ public void Directives_can_have_a_value_which_is_everything_after_the_first_colo
             string expectedKey,
             string expectedValue)
         {
-            var option = new Option("-y");
+            var option = new Option<bool>("-y");
 
             var result = option.Parse($"{directive} -y");
 
@@ -83,7 +83,7 @@ public void Directives_can_have_a_value_which_is_everything_after_the_first_colo
         [Fact]
         public void Directives_without_a_value_specified_have_a_value_of_empty_string()
         {
-            var option = new Option("-y");
+            var option = new Option<bool>("-y");
 
             var result = option.Parse("[parse] -y");
 
@@ -96,7 +96,7 @@ public void Directives_without_a_value_specified_have_a_value_of_empty_string()
         [InlineData("[:value]")]
         public void Directives_must_have_a_non_empty_key(string directive)
         {
-            var option = new Option("-a");
+            var option = new Option<bool>("-a");
 
             var result = option.Parse($"{directive} -a");
 
@@ -110,7 +110,7 @@ public void Directives_must_have_a_non_empty_key(string directive)
         [InlineData("[parse ]")]
         public void Directives_cannot_contain_spaces(object value)
         {
-            var option = new Option("-a");
+            var option = new Option<bool>("-a");
 
             var result = option.Parse($"{value} -a");
 
@@ -120,7 +120,7 @@ public void Directives_cannot_contain_spaces(object value)
         [Fact]
         public void When_a_directive_is_specified_more_than_once_then_its_values_are_aggregated()
         {
-            var option = new Option("-a");
+            var option = new Option<bool>("-a");
 
             var result = option.Parse("[directive:one] [directive:two] -a");
 
diff --git a/src/System.CommandLine.Tests/ParserTests.cs b/src/System.CommandLine.Tests/ParserTests.cs
index 0e7eaea8bf..0c68f14d23 100644
--- a/src/System.CommandLine.Tests/ParserTests.cs
+++ b/src/System.CommandLine.Tests/ParserTests.cs
@@ -11,9 +11,6 @@
 using System.Linq;
 using FluentAssertions.Common;
 using Xunit;
-using System.ComponentModel;
-using System.Globalization;
-using System.Threading.Tasks;
 using Xunit.Abstractions;
 
 namespace System.CommandLine.Tests
@@ -30,8 +27,8 @@ public ParserTests(ITestOutputHelper output)
         [Fact]
         public void An_option_can_be_checked_by_object_instance()
         {
-            var option = new Option("--flag");
-            var option2 = new Option("--flag2");
+            var option = new Option<bool>("--flag");
+            var option2 = new Option<bool>("--flag2");
             var result = new Parser(new RootCommand { option, option2 })
                 .Parse("--flag");
 
@@ -42,9 +39,9 @@ public void An_option_can_be_checked_by_object_instance()
         [Fact]
         public void Two_options_are_parsed_correctly()
         {
-            var optionOne = new Option(new[] { "-o", "--one" });
+            var optionOne = new Option<bool>(new[] { "-o", "--one" });
 
-            var optionTwo = new Option(new[] { "-t", "--two" });
+            var optionTwo = new Option<bool>(new[] { "-t", "--two" });
 
             var result = new Parser(
                     new RootCommand
@@ -101,7 +98,7 @@ public void Long_form_options_can_be_specified_using_equals_delimiter()
         [Fact]
         public void Short_form_options_can_be_specified_using_colon_delimiter()
         {
-            var option = new Option("-x") { Arity = ArgumentArity.ExactlyOne };
+            var option = new Option<string>("-x");
 
             var result = option.Parse("-x:some-value");
 
@@ -126,9 +123,9 @@ public void Long_form_options_can_be_specified_using_colon_delimiter()
         public void Option_short_forms_can_be_bundled()
         {
             var command = new Command("the-command");
-            command.AddOption(new Option("-x"));
-            command.AddOption(new Option("-y"));
-            command.AddOption(new Option("-z"));
+            command.AddOption(new Option<bool>("-x"));
+            command.AddOption(new Option<bool>("-y"));
+            command.AddOption(new Option<bool>("-z"));
 
             var result = command.Parse("the-command -xyz");
 
@@ -146,9 +143,9 @@ public void Options_short_forms_do_not_get_unbundled_if_unbundling_is_turned_off
                          {
                              new Command("the-command")
                              {
-                                 new Option("-x"),
-                                 new Option("-y"),
-                                 new Option("-z")
+                                 new Option<bool>("-x"),
+                                 new Option<bool>("-y"),
+                                 new Option<bool>("-z")
                              }
                          })
                          .EnablePosixBundling(false)
@@ -167,10 +164,10 @@ public void Option_long_forms_do_not_get_unbundled()
             var parser = new Parser(
                 new Command("the-command")
                 {
-                    new Option("--xyz"),
-                    new Option("-x"),
-                    new Option("-y"),
-                    new Option("-z")
+                    new Option<bool>("--xyz"),
+                    new Option<bool>("-x"),
+                    new Option<bool>("-y"),
+                    new Option<bool>("-z")
                 });
 
             var result = parser.Parse("the-command --xyz");
@@ -186,7 +183,7 @@ public void Option_long_forms_do_not_get_unbundled()
         public void Options_do_not_get_unbundled_unless_all_resulting_options_would_be_valid_for_the_current_command()
         {
             var outer = new Command("outer");
-            outer.AddOption(new Option("-a"));
+            outer.AddOption(new Option<bool>("-a"));
             var inner = new Command("inner")
             {
                 new Argument
@@ -194,8 +191,8 @@ public void Options_do_not_get_unbundled_unless_all_resulting_options_would_be_v
                     Arity = ArgumentArity.ZeroOrMore
                 }
             };
-            inner.AddOption(new Option("-b"));
-            inner.AddOption(new Option("-c"));
+            inner.AddOption(new Option<bool>("-b"));
+            inner.AddOption(new Option<bool>("-c"));
             outer.AddCommand(inner);
 
             var parser = new Parser(outer);
@@ -213,8 +210,8 @@ public void Options_do_not_get_unbundled_unless_all_resulting_options_would_be_v
         public void Required_option_arguments_are_not_unbundled()
         {
             var optionA = new Option<string>("-a");
-            var optionB = new Option("-b");
-            var optionC = new Option("-c");
+            var optionB = new Option<bool>("-b");
+            var optionC = new Option<bool>("-c");
 
             var command = new RootCommand
             {
@@ -795,7 +792,7 @@ public void A_root_command_can_be_omitted_from_the_parsed_args()
             {
                 new Command("inner")
                 {
-                    new Option("-x") { Arity = ArgumentArity.ExactlyOne }
+                    new Option<string>("-x")
                 }
             };
 
@@ -812,7 +809,7 @@ public void A_root_command_can_match_a_full_path_to_an_executable()
             {
                 new Command("inner")
                 {
-                    new Option("-x") { Arity = ArgumentArity.ExactlyOne }
+                    new Option<string>("-x")
                 }
             };
 
@@ -830,7 +827,7 @@ public void A_renamed_RootCommand_can_be_omitted_from_the_parsed_args()
                               {
                                   new Command("inner")
                                   {
-                                      new Option("-x") { Arity = ArgumentArity.ExactlyOne }
+                                      new Option<string>("-x")
                                   }
                               };
             rootCommand.Name = "outer";
@@ -1395,7 +1392,7 @@ public void When_a_command_line_has_unmatched_tokens_they_are_not_applied_to_sub
             {
                 TreatUnmatchedTokensAsErrors = false
             };
-            var optionX = new Option("-x") { Arity = ArgumentArity.ExactlyOne };
+            var optionX = new Option<string>("-x");
             command.AddOption(optionX);
             var optionY = new Option("-y") { Arity = ArgumentArity.ExactlyOne };
             command.AddOption(optionY);
diff --git a/src/System.CommandLine/Option.cs b/src/System.CommandLine/Option.cs
index 77ff4c47c1..508d8bfb4f 100644
--- a/src/System.CommandLine/Option.cs
+++ b/src/System.CommandLine/Option.cs
@@ -19,6 +19,10 @@ public class Option : IdentifierSymbol, IValueDescriptor
         private List<ValidateSymbolResult<OptionResult>>? _validators;
         private Argument? _argument;
 
+        public Option(string name) : this(name, description: null){}
+        
+        public Option(string name, string description) : this(name, description, argumentType: null){}
+
         /// <summary>
         /// Initializes a new instance of the <see cref="Option"/> class.
         /// </summary>

From 55c90353f5aa792c449a058ec4c7d39e9b660ca1 Mon Sep 17 00:00:00 2001
From: Jon Sequeira <jonsequeira@gmail.com>
Date: Sun, 13 Mar 2022 17:07:44 -0700
Subject: [PATCH 02/11] wip

---
 .../TableRenderingTests.cs                    |  16 +--
 .../Binding/TypeConversionTests.cs            | 115 +-----------------
 .../CompletionTests.cs                        |  16 +--
 .../GlobalOptionTests.cs                      |  18 ---
 .../Help/HelpBuilderTests.cs                  |  70 ++++++-----
 .../VersionOptionTests.cs                     |   2 +-
 src/System.CommandLine/Argument.cs            |   1 +
 src/System.CommandLine/Option.cs              |  16 ++-
 8 files changed, 74 insertions(+), 180 deletions(-)

diff --git a/src/System.CommandLine.Rendering.Tests/TableRenderingTests.cs b/src/System.CommandLine.Rendering.Tests/TableRenderingTests.cs
index f8574deed5..91febb9353 100644
--- a/src/System.CommandLine.Rendering.Tests/TableRenderingTests.cs
+++ b/src/System.CommandLine.Rendering.Tests/TableRenderingTests.cs
@@ -34,8 +34,8 @@ public TableRenderingTests(ITestOutputHelper output)
         public void A_row_is_written_for_each_item_and_a_header_for_each_column(OutputMode outputMode)
         {
             var options = new[] {
-                new Option("-s", "a short option"),
-                new Option("--very-long", "a long option")
+                new Option<string>("-s", "a short option"),
+                new Option<string>("--very-long", "a long option")
             };
 
             var view = new OptionsHelpView(options);
@@ -57,8 +57,8 @@ public void A_row_is_written_for_each_item_and_a_header_for_each_column_in_file_
         {
             var options = new[]
                           {
-                              new Option("-s", "a short option"),
-                              new Option("--very-long", "a long option")
+                              new Option<string>("-s", "a short option"),
+                              new Option<string>("--very-long", "a long option")
                           };
 
             var view = new OptionsHelpView(options);
@@ -80,8 +80,8 @@ public void A_row_is_written_for_each_item_and_a_header_for_each_column_in_file_
         public void Column_widths_are_aligned_to_the_longest_cell(OutputMode outputMode)
         {
             var options = new[] {
-                new Option("-s", "an option"),
-                new Option("--very-long", "an option")
+                new Option<string>("-s", "an option"),
+                new Option<string>("--very-long", "an option")
             };
 
             var view = new OptionsHelpView(options);
@@ -101,8 +101,8 @@ public void Column_widths_are_aligned_to_the_longest_cell(OutputMode outputMode)
         public void Column_widths_are_aligned_to_the_longest_cell_in_file_mode()
         {
             var options = new[] {
-                new Option("-s", "an option"),
-                new Option("--very-long", "an option")
+                new Option<string>("-s", "an option"),
+                new Option<string>("--very-long", "an option")
             };
 
             var view = new OptionsHelpView(options);
diff --git a/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs b/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
index 56474021db..37290428b5 100644
--- a/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
+++ b/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
@@ -235,41 +235,7 @@ public void Generic_option_bool_parses_when_passed_to_non_generic_GetValueForOpt
 
             parseResult.GetValueForOption((Option)option).Should().Be(true);
         }
-
-        [Fact]
-        public void By_default_an_option_with_zero_or_one_argument_parses_as_the_argument_string_value()
-        {
-            var option = new Option("-x", arity: ArgumentArity.ZeroOrOne);
-
-            var command = new Command("the-command")
-            {
-                option
-            };
-
-            var result = command.Parse("the-command -x the-argument");
-
-            result.GetValueForOption(option)
-                  .Should()
-                  .Be("the-argument");
-        }
-
-        [Fact]
-        public void By_default_an_option_with_exactly_one_argument_parses_as_the_argument_string_value()
-        {
-            var option = new Option("-x", arity: ArgumentArity.ExactlyOne);
-
-            var command = new Command("the-command")
-            {
-                option
-            };
-
-            var result = command.Parse("the-command -x the-argument");
-
-            result.GetValueForOption(option)
-                  .Should()
-                  .Be("the-argument");
-        }
-
+        
         [Fact]
         public void When_exactly_one_argument_is_expected_and_none_are_provided_then_getting_value_throws()
         {
@@ -291,81 +257,7 @@ public void When_exactly_one_argument_is_expected_and_none_are_provided_then_get
                     .Should()
                     .Be("Required argument missing for option: '-x'.");
         }
-
-        [Fact]
-        public void When_zero_or_more_arguments_of_unspecified_type_are_expected_and_none_are_provided_then_getting_value_returns_an_empty_sequence_of_strings()
-        {
-            var option = new Option("-x", arity: ArgumentArity.ZeroOrMore);
-
-            var command = new Command("the-command")
-            {
-                option
-            };
-
-            var result = command.Parse("the-command -x");
-
-            result.GetValueForOption(option)
-                  .Should()
-                  .BeAssignableTo<IReadOnlyCollection<string>>()
-                  .Which
-                  .Should()
-                  .BeEmpty();
-        }
-
-        [Fact]
-        public void When_one_or_more_arguments_of_unspecified_type_are_expected_and_none_are_provided_then_getting_value_throws()
-        {
-            var option = new Option("-x", arity: ArgumentArity.OneOrMore);
-
-            var command = new Command("the-command")
-            {
-                option
-            };
-
-            var result = command.Parse("the-command -x");
-
-            Action getValue = () => result.GetValueForOption(option);
-
-            getValue.Should()
-                    .Throw<InvalidOperationException>()
-                    .Which
-                    .Message
-                    .Should()
-                    .Be("Required argument missing for option: '-x'.");
-        }
-
-        [Fact]
-        public void By_default_an_option_that_allows_multiple_arguments_and_is_passed_multiple_arguments_parses_as_a_sequence_of_strings()
-        {
-            var option = new Option("-x", arity: ArgumentArity.ZeroOrMore);
-
-            var command = new Command("the-command")
-            {
-                option
-            };
-
-            command.Parse("the-command -x arg1 -x arg2")
-                   .GetValueForOption(option)
-                   .Should()
-                   .BeEquivalentTo(new[] { "arg1", "arg2" });
-        }
-
-        [Fact]
-        public void By_default_an_option_that_allows_multiple_arguments_and_is_passed_one_argument_parses_as_a_sequence_of_strings()
-        {
-            var option = new Option("-x", arity: ArgumentArity.ZeroOrMore);
-
-            var command = new Command("the-command")
-            {
-                option
-            };
-
-            command.Parse("the-command -x arg1")
-                   .GetValueForOption(option)
-                   .Should()
-                   .BeEquivalentTo(new[] { "arg1" });
-        }
-
+        
         [Theory]
         [InlineData("c -a o c c")]
         [InlineData("c c -a o c")]
@@ -856,7 +748,8 @@ public void Max_arity_greater_than_1_converts_to_enumerable_types(
             int maxArity,
             Type argumentType)
         {
-            var option = new Option("--items", argumentType: argumentType, arity: new ArgumentArity(minArity, maxArity));
+            var arity = new ArgumentArity(minArity, maxArity);
+            var option = new Option("--items", argumentType: argumentType, arity: arity);
 
             var command = new RootCommand
             {
diff --git a/src/System.CommandLine.Tests/CompletionTests.cs b/src/System.CommandLine.Tests/CompletionTests.cs
index 15554e8443..c8abfa162f 100644
--- a/src/System.CommandLine.Tests/CompletionTests.cs
+++ b/src/System.CommandLine.Tests/CompletionTests.cs
@@ -41,9 +41,9 @@ public void Command_GetCompletions_returns_available_option_aliases()
         {
             var command = new Command("command")
             {
-                new Option("--one", "option one"),
-                new Option("--two", "option two"),
-                new Option("--three", "option three")
+                new Option<string>("--one", "option one"),
+                new Option<string>("--two", "option two"),
+                new Option<string>("--three", "option three")
             };
 
             var completions = command.GetCompletions();
@@ -59,8 +59,8 @@ public void Command_GetCompletions_returns_available_option_aliases_for_global_o
         {
             var subcommand = new Command("command")
             {
-                new Option("--one", "option one"),
-                new Option("--two", "option two")
+                new Option<string>("--one", "option one"),
+                new Option<string>("--two", "option two")
             };
 
             var rootCommand = new RootCommand
@@ -68,7 +68,7 @@ public void Command_GetCompletions_returns_available_option_aliases_for_global_o
                 subcommand
             };
 
-            rootCommand.AddGlobalOption(new Option("--three", "option three"));
+            rootCommand.AddGlobalOption(new Option<string>("--three", "option three"));
 
             var completions = subcommand.GetCompletions();
 
@@ -118,7 +118,7 @@ public void Command_GetCompletions_returns_available_subcommands_and_option_alia
             var command = new Command("command")
             {
                 new Command("subcommand", "subcommand"),
-                new Option("--option", "option"),
+                new Option<bool>("--option", "option"),
                 new Argument
                 {
                     Arity = ArgumentArity.OneOrMore,
@@ -426,7 +426,7 @@ public void An_option_can_be_hidden_from_completions_by_setting_IsHidden_to_true
                 {
                     IsHidden = true
                 },
-                new Option("-n", "Not hidden")
+                new Option<string>("-n", "Not hidden")
             };
 
             var completions = command.Parse("the-command ").GetCompletions();
diff --git a/src/System.CommandLine.Tests/GlobalOptionTests.cs b/src/System.CommandLine.Tests/GlobalOptionTests.cs
index ff20a30e74..f6884378fb 100644
--- a/src/System.CommandLine.Tests/GlobalOptionTests.cs
+++ b/src/System.CommandLine.Tests/GlobalOptionTests.cs
@@ -1,10 +1,6 @@
 // Copyright (c) .NET Foundation and contributors. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
-// Copyright (c) .NET Foundation and contributors. All rights reserved.
-// Licensed under the MIT license. See LICENSE file in the project root for full license information.
-
-using System.Threading.Tasks;
 using FluentAssertions;
 using Xunit;
 
@@ -12,20 +8,6 @@ namespace System.CommandLine.Tests
 {
     public class GlobalOptionTests
     {
-        [Fact]
-        public void Global_options_may_be_added_with_aliases_that_conflict_with_local_options()
-        {
-            var command = new Command("the-command")
-            {
-                new Option("--same")
-            };
-
-            command
-                .Invoking(c => c.AddGlobalOption(new Option("--same")))
-                .Should()
-                .NotThrow<ArgumentException>();
-        }
-
         [Fact]
         public void Global_options_appear_in_options_list()
         {
diff --git a/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs b/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
index d4e74bcc06..9853a1096d 100644
--- a/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
+++ b/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
@@ -208,7 +208,7 @@ public void Usage_section_for_subcommand_shows_names_of_parent_commands()
             outer.AddCommand(inner);
             var innerEr = new Command("inner-er", "the inner-er command");
             inner.AddCommand(innerEr);
-            innerEr.AddOption(new Option("--some-option", "some option"));
+            innerEr.AddOption(new Option<string>("--some-option", "some option"));
             var rootCommand = new RootCommand();
             rootCommand.Add(outer);
 
@@ -226,7 +226,7 @@ public void Usage_section_for_subcommand_shows_arguments_for_subcommand_and_pare
         {
             var inner = new Command("inner", "command help")
             {
-                new Option("-v", "Sets the verbosity"),
+                new Option<string>("-v", "Sets the verbosity"),
                 new Argument<string[]>
                 {
                     Name = "inner-args"
@@ -257,7 +257,7 @@ public void Usage_section_does_not_show_additional_arguments_when_TreatUnmatched
                 "some-command",
                 "Does something");
             command.AddOption(
-                new Option("-x", "Indicates whether x"));
+                new Option<string>("-x", "Indicates whether x"));
 
             _helpBuilder.Write(command, _console);
 
@@ -270,7 +270,7 @@ public void Usage_section_does_not_show_additional_arguments_when_TreatUnmatched
             var command = new RootCommand();
             var subcommand = new Command("some-command", "Does something");
             command.AddCommand(subcommand);
-            subcommand.AddOption(new Option("-x", "Indicates whether x"));
+            subcommand.AddOption(new Option<string>("-x", "Indicates whether x"));
             subcommand.TreatUnmatchedTokensAsErrors = true;
 
             _helpBuilder.Write(subcommand, _console);
@@ -284,7 +284,7 @@ public void Usage_section_shows_additional_arguments_when_TreatUnmatchedTokensAs
             var command = new RootCommand();
             var subcommand = new Command("some-command", "Does something");
             command.AddCommand(subcommand);
-            subcommand.AddOption(new Option("-x", "Indicates whether x"));
+            subcommand.AddOption(new Option<string>("-x", "Indicates whether x"));
             subcommand.TreatUnmatchedTokensAsErrors = false;
 
             _helpBuilder.Write(subcommand, _console);
@@ -449,7 +449,7 @@ public void Arguments_section_is_not_included_if_there_are_only_options_with_arg
         {
             var command = new Command("command")
             {
-                new Option("-v", "Sets the verbosity.", arity: ArgumentArity.ExactlyOne)
+                new Option<string>("-v", "Sets the verbosity.")
                 {
                     ArgumentHelpName = "argument for options"
                 }
@@ -755,17 +755,21 @@ public void Command_argument_usage_indicates_enums_values(Type type)
         }
 
         [Theory]
-        [InlineData(typeof(bool))]
-        [InlineData(typeof(bool?))]
-        public void Option_argument_usage_is_empty_for_boolean_values(Type type)
+        [InlineData(true)]
+        [InlineData(false)]
+        public void Option_argument_usage_is_empty_for_boolean_values(bool nullable)
         {
             var description = "This is the option description";
 
+            Option option = nullable
+                                ? new Option<bool?>("--opt", description)
+                                : new Option<bool>("--opt", description);
+
             var command = new Command(
                 "outer", "Help text for the outer command")
-                          {
-                              new Option("--opt", description, argumentType: type)
-                          };
+            {
+                option
+            };
 
             HelpBuilder helpBuilder = GetHelpBuilder(SmallMaxWidth);
 
@@ -796,17 +800,21 @@ public void Command_arguments_show_argument_name_in_first_column()
         }
 
         [Theory]
-        [InlineData(typeof(FileAccess))]
-        [InlineData(typeof(FileAccess?))]
-        public void Option_argument_first_column_indicates_enums_values(Type type)
+        [InlineData(true)]
+        [InlineData(false)]
+        public void Option_argument_first_column_indicates_enums_values(bool nullable)
         {
             var description = "This is the argument description";
 
+            Option option = nullable
+                                ? new Option<FileAccess?>("--opt", description)
+                                : new Option<FileAccess>("--opt", description);
+
             var command = new Command(
-                              "outer", "Help text for the outer command")
-                          {
-                              new Option("--opt", description, argumentType: type)
-                          };
+                "outer", "Help text for the outer command")
+            {
+                option
+            };
 
             HelpBuilder helpBuilder = GetHelpBuilder(SmallMaxWidth);
 
@@ -860,7 +868,7 @@ public void Help_does_not_show_default_value_for_argument_when_default_value_is_
         [Fact]
         public void Help_does_not_show_default_value_for_option_when_default_value_is_empty()
         {
-            var option = new Option("-x", description: "The option description");
+            var option = new Option<string>("-x", description: "The option description");
             option.SetDefaultValue("");
 
             var command = new Command("the-command", "The command description")
@@ -964,8 +972,8 @@ public void Options_section_includes_option_with_empty_description()
         {
             var command = new Command("the-command", "Does things.")
                           {
-                              new Option("-x"),
-                              new Option("-n")
+                              new Option<string>("-x"),
+                              new Option<string>("-n")
                           };
 
             _helpBuilder.Write(command, _console);
@@ -979,11 +987,11 @@ public void Options_section_includes_option_with_empty_description()
         public void Options_section_does_not_contain_option_with_HelpDefinition_that_IsHidden()
         {
             var command = new Command("the-command");
-            command.AddOption(new Option("-x", "Is Hidden")
+            command.AddOption(new Option<string>("-x", "Is Hidden")
             {
                 IsHidden = true
             });
-            command.AddOption(new Option("-n", "Not Hidden")
+            command.AddOption(new Option<string>("-n", "Not Hidden")
             {
                 IsHidden = false
             });
@@ -1089,9 +1097,9 @@ public void Options_section_properly_wraps_description()
 
             var command = new Command("test-command", "Help text for the command")
             {
-                new Option("-x", "Option with a short description"),
+                new Option<string>("-x", "Option with a short description"),
                 new Option(new[] { "-a", "--aaa" }, longOptionText),
-                new Option("-y", "Option with a short description"),
+                new Option<string>("-y", "Option with a short description"),
             };
 
             HelpBuilder helpBuilder = GetHelpBuilder(SmallMaxWidth);
@@ -1114,9 +1122,9 @@ public void Options_section_properly_wraps_description_when_long_default_value_i
 
             var command = new Command("test-command", "Help text for the command")
             {
-                new Option("-x", "Option with a short description"),
+                new Option<string>("-x", "Option with a short description"),
                 new Option(new[] { "-a", "--aaa" }, longOptionText, getDefaultValue: () => "the quick brown fox jumps over the lazy dog"),
-                new Option("-y", "Option with a short description"),
+                new Option<string>("-y", "Option with a short description"),
             };
 
             HelpBuilder helpBuilder = GetHelpBuilder(SmallMaxWidth);
@@ -1138,7 +1146,7 @@ public void Options_section_properly_wraps()
 
             var command = new RootCommand
             {
-                new Option(alias, description)
+                new Option<bool>(alias, description)
             };
 
             HelpBuilder helpBuilder = GetHelpBuilder(SmallMaxWidth);
@@ -1158,7 +1166,7 @@ public void Required_options_are_indicated()
         {
             var command = new RootCommand
             {
-                new Option("--required")
+                new Option<bool>("--required")
                 {
                     IsRequired = true
                 }
@@ -1346,7 +1354,7 @@ public void Subcommand_help_does_not_include_names_of_sibling_commands()
                             new Command(
                                 "inner-er", "inner-er description")
                             {
-                                new Option("some-option",
+                                new Option<string>("some-option",
                                            "some-option description")
                             }
                         };
diff --git a/src/System.CommandLine.Tests/VersionOptionTests.cs b/src/System.CommandLine.Tests/VersionOptionTests.cs
index d813c6144e..046b863876 100644
--- a/src/System.CommandLine.Tests/VersionOptionTests.cs
+++ b/src/System.CommandLine.Tests/VersionOptionTests.cs
@@ -75,7 +75,7 @@ public async Task When_the_version_option_is_specified_and_there_are_default_opt
         {
             var rootCommand = new RootCommand
             {
-                new Option("-x", getDefaultValue: () => true)
+                new Option<bool>("-x")
             };
             rootCommand.SetHandler(() => { });
 
diff --git a/src/System.CommandLine/Argument.cs b/src/System.CommandLine/Argument.cs
index 5d9c0d280d..7ac9603a2b 100644
--- a/src/System.CommandLine/Argument.cs
+++ b/src/System.CommandLine/Argument.cs
@@ -28,6 +28,7 @@ public class Argument : Symbol, IValueDescriptor
         /// </summary>
         public Argument()
         {
+            // FIX: (Argument) make this protected
         }
 
         /// <summary>
diff --git a/src/System.CommandLine/Option.cs b/src/System.CommandLine/Option.cs
index 508d8bfb4f..8d82d528b4 100644
--- a/src/System.CommandLine/Option.cs
+++ b/src/System.CommandLine/Option.cs
@@ -19,9 +19,19 @@ public class Option : IdentifierSymbol, IValueDescriptor
         private List<ValidateSymbolResult<OptionResult>>? _validators;
         private Argument? _argument;
 
-        public Option(string name) : this(name, description: null){}
-        
-        public Option(string name, string description) : this(name, description, argumentType: null){}
+        // FIX: (Option) delete temp constructors
+
+        public Option(string name) : this(name, description: null)
+        {
+        }
+
+        public Option(string name, ArgumentArity arity) : this(name, description: null, arity: arity)
+        {
+        }
+
+        public Option(string name, Func<object?>? getDefaultValue) : this(name,null, getDefaultValue: getDefaultValue)
+        {
+        }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Option"/> class.

From 9158be6085432121e2ae62a2be5466868596a2ec Mon Sep 17 00:00:00 2001
From: Jon Sequeira <jonsequeira@gmail.com>
Date: Mon, 14 Mar 2022 11:20:22 -0700
Subject: [PATCH 03/11] wip

---
 .../CommandLine/Perf_Parser_Options_Bare.cs   |   5 +-
 .../Perf_Parser_Options_With_Arguments.cs     |   3 +-
 .../CommandLine/Perf_Suggestions.cs           |   4 +-
 .../ModelBindingCommandHandlerTests.cs        |  18 ---
 .../ParameterBindingTests.cs                  |   2 +-
 .../Binding/TypeConversionTests.cs            |   8 +-
 .../CommandLineConfigurationTests.cs          |   4 +-
 src/System.CommandLine.Tests/CommandTests.cs  |   4 +-
 .../CompletionTests.cs                        |  67 +++-----
 .../Invocation/TypoCorrectionTests.cs         |  18 +--
 src/System.CommandLine.Tests/OptionTests.cs   |  67 +++-----
 .../ParseDiagramTests.cs                      |  13 +-
 src/System.CommandLine/IdentifierSymbol.cs    |   2 +-
 .../Parsing/ParseResultExtensions.cs          | 145 ++++++++++--------
 14 files changed, 155 insertions(+), 205 deletions(-)

diff --git a/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_Options_Bare.cs b/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_Options_Bare.cs
index b4b69698db..ca6d9d3a70 100644
--- a/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_Options_Bare.cs
+++ b/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_Options_Bare.cs
@@ -22,8 +22,9 @@ public class Perf_Parser_Options_Bare
         private IEnumerable<Option> GenerateTestOptions(int count, ArgumentArity arity)
             => Enumerable.Range(0, count)
                          .Select(i =>
-                                     new Option($"-option{i}", arity: arity)
+                                     new Option<string>($"-option{i}")
                                      {
+                                         Arity = arity,
                                          Description = $"Description for -option {i} ...."
                                      }
                          );
@@ -50,7 +51,7 @@ public void SetupTestOptions()
         [Benchmark]
         public Parser ParserFromOptions_Ctor()
         {
-            return Utils.CreateParser(_testSymbols);
+            return _testSymbols.CreateParser();
         }
 
         [GlobalSetup(Target = nameof(ParserFromOptions_Parse))]
diff --git a/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_Options_With_Arguments.cs b/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_Options_With_Arguments.cs
index 78492ea96b..63a4e9c996 100644
--- a/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_Options_With_Arguments.cs
+++ b/src/System.CommandLine.Benchmarks/CommandLine/Perf_Parser_Options_With_Arguments.cs
@@ -20,8 +20,9 @@ public class Perf_Parser_Options_With_Arguments
 
         private IEnumerable<Option> GenerateTestOptions(int count, ArgumentArity arity)
             => Enumerable.Range(0, count)
-                         .Select(i => new Option($"-option{i}", arity: arity)
+                         .Select(i => new Option<string>($"-option{i}")
                              {
+                                 Arity = arity,
                                  Description = $"Description for -option {i} ...."
                              }
                          );
diff --git a/src/System.CommandLine.Benchmarks/CommandLine/Perf_Suggestions.cs b/src/System.CommandLine.Benchmarks/CommandLine/Perf_Suggestions.cs
index ac7aa09a92..191260da57 100644
--- a/src/System.CommandLine.Benchmarks/CommandLine/Perf_Suggestions.cs
+++ b/src/System.CommandLine.Benchmarks/CommandLine/Perf_Suggestions.cs
@@ -29,7 +29,7 @@ private string[] GenerateSuggestionsArray(int count)
 
         private IEnumerable<Option> GenerateOptionsArray(int count)
             => Enumerable.Range(0, count)
-                         .Select(i => new Option($"suggestion{i}"));
+                         .Select(i => new Option<string>($"suggestion{i}"));
 
         [Params(1, 5, 20, 100)]
         public int TestSuggestionsCount;
@@ -37,7 +37,7 @@ private IEnumerable<Option> GenerateOptionsArray(int count)
         [GlobalSetup(Target = nameof(SuggestionsFromSymbol))]
         public void Setup_FromSymbol()
         {
-            _testSymbol = new Option("--hello", arity: ArgumentArity.ExactlyOne)
+            _testSymbol = new Option<string>("--hello")
                 .AddCompletions(GenerateSuggestionsArray(TestSuggestionsCount));
         }
 
diff --git a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs
index 352c0279c4..9c715838a0 100644
--- a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs
+++ b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs
@@ -49,24 +49,6 @@ public async Task Unspecified_option_arguments_with_no_default_value_are_bound_t
 
         boundValue.Should().Be(expectedValue);
     }
-
-    [Fact]
-    public async Task When_argument_type_is_not_known_until_binding_then_bool_parameter_is_bound_correctly()
-    {
-        bool? received = null;
-
-        var handler = CommandHandler.Create((bool x) => received = x);
-
-        var root = new RootCommand
-        {
-            new Option("-x")
-        };
-        root.Handler = handler;
-
-        await root.InvokeAsync("-x");
-
-        received.Should().BeTrue();
-    }
     
     [Theory]
     [InlineData(typeof(ClassWithCtorParameter<int>), false)]
diff --git a/src/System.CommandLine.NamingConventionBinder.Tests/ParameterBindingTests.cs b/src/System.CommandLine.NamingConventionBinder.Tests/ParameterBindingTests.cs
index 74b7ecedbc..55f1fd3028 100644
--- a/src/System.CommandLine.NamingConventionBinder.Tests/ParameterBindingTests.cs
+++ b/src/System.CommandLine.NamingConventionBinder.Tests/ParameterBindingTests.cs
@@ -73,7 +73,7 @@ void Execute(string name, int AGE)
         }
 
         var command = new Command("command");
-        command.AddOption(new Option("--NAME", arity: ArgumentArity.ExactlyOne));
+        command.AddOption(new Option<string>("--NAME"));
         command.AddOption(new Option<int>("--age"));
         command.Handler = CommandHandler.Create<string, int>(Execute);
 
diff --git a/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs b/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
index 37290428b5..d37eccf161 100644
--- a/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
+++ b/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
@@ -283,9 +283,9 @@ public void When_command_argument_has_arity_greater_than_one_it_captures_argumen
         }
 
         [Fact]
-        public void The_default_value_of_an_option_with_no_arguments_is_true()
+        public void The_default_value_of_a_bool_option_with_no_arguments_is_true()
         {
-            var option = new Option("-x");
+            var option = new Option<bool>("-x");
 
             var command =
                 new Command("the-command")
@@ -301,9 +301,9 @@ public void The_default_value_of_an_option_with_no_arguments_is_true()
         }
 
         [Fact]
-        public void By_default_an_option_without_arguments_parses_as_false_when_it_is_not_applied()
+        public void By_default_a_bool_option_without_arguments_parses_as_false_when_it_is_not_applied()
         {
-            var option = new Option("-x");
+            var option = new Option<bool>("-x");
 
             var command = new Command("something")
             {
diff --git a/src/System.CommandLine.Tests/CommandLineConfigurationTests.cs b/src/System.CommandLine.Tests/CommandLineConfigurationTests.cs
index 2559fc6ab0..70fbf85af0 100644
--- a/src/System.CommandLine.Tests/CommandLineConfigurationTests.cs
+++ b/src/System.CommandLine.Tests/CommandLineConfigurationTests.cs
@@ -117,7 +117,7 @@ public void ThrowIfInvalid_throws_if_there_are_duplicate_sibling_subcommand_alia
     [Fact]
     public void ThrowIfInvalid_throws_if_sibling_command_and_option_aliases_collide_on_the_root_command()
     {
-        var option = new Option("dupe");
+        var option = new Option<string>("dupe");
         var command = new Command("not-a-dupe");
         command.AddAlias("dupe");
 
@@ -142,7 +142,7 @@ public void ThrowIfInvalid_throws_if_sibling_command_and_option_aliases_collide_
     [Fact]
     public void ThrowIfInvalid_throws_if_sibling_command_and_option_aliases_collide_on_a_subcommand()
     {
-        var option = new Option("dupe");
+        var option = new Option<string>("dupe");
         var command = new Command("not-a-dupe");
         command.AddAlias("dupe");
 
diff --git a/src/System.CommandLine.Tests/CommandTests.cs b/src/System.CommandLine.Tests/CommandTests.cs
index 9fc6f684ac..32858bb53e 100644
--- a/src/System.CommandLine.Tests/CommandTests.cs
+++ b/src/System.CommandLine.Tests/CommandTests.cs
@@ -155,7 +155,7 @@ public void When_a_command_is_created_with_an_alias_that_contains_whitespace_the
                   .Which
                   .Message
                   .Should()
-                  .Contain($"Command alias cannot contain whitespace: \"{alias}\"");
+                  .Contain($"Alias cannot contain whitespace: \"{alias}\"");
         }
 
         [Theory]
@@ -175,7 +175,7 @@ public void When_a_command_alias_is_added_and_contains_whitespace_then_an_inform
                 .Which
                 .Message
                 .Should()
-                .Contain($"Command alias cannot contain whitespace: \"{alias}\"");
+                .Contain($"Alias cannot contain whitespace: \"{alias}\"");
         }
 
         [Theory]
diff --git a/src/System.CommandLine.Tests/CompletionTests.cs b/src/System.CommandLine.Tests/CompletionTests.cs
index c8abfa162f..9ad79f32df 100644
--- a/src/System.CommandLine.Tests/CompletionTests.cs
+++ b/src/System.CommandLine.Tests/CompletionTests.cs
@@ -422,7 +422,7 @@ public void An_option_can_be_hidden_from_completions_by_setting_IsHidden_to_true
         {
             var command = new Command("the-command")
             {
-                new Option("--hide-me")
+                new Option<string>("--hide-me")
                 {
                     IsHidden = true
                 },
@@ -439,10 +439,8 @@ public void Parser_options_can_supply_context_sensitive_matches()
         {
             var parser = new RootCommand
             {
-                new Option("--bread", arity: ArgumentArity.ExactlyOne)
-                    .FromAmong("wheat", "sourdough", "rye"),
-                new Option("--cheese", arity: ArgumentArity.ExactlyOne)
-                    .FromAmong("provolone", "cheddar", "cream cheese")
+                new Option<string>("--bread").FromAmong("wheat", "sourdough", "rye"),
+                new Option<string>("--cheese").FromAmong("provolone", "cheddar", "cream cheese")
             };
 
             var commandLine = "--bread";
@@ -532,9 +530,9 @@ public void Option_GetCompletions_can_be_based_on_the_proximate_option()
             var parser = new Parser(
                 new Command("outer")
                 {
-                    new Option("--one"),
-                    new Option("--two"),
-                    new Option("--three")
+                    new Option<string>("--one"),
+                    new Option<string>("--two"),
+                    new Option<string>("--three")
                 });
 
             var commandLine = "outer";
@@ -552,10 +550,8 @@ public void Argument_completions_can_be_based_on_the_proximate_option()
             var parser = new Parser(
                 new Command("outer")
                 {
-                    new Option("--one", arity: ArgumentArity.ExactlyOne)
-                        .FromAmong("one-a", "one-b"),
-                    new Option("--two", arity: ArgumentArity.ExactlyOne)
-                        .FromAmong("two-a", "two-b")
+                    new Option<string>("--one").FromAmong("one-a", "one-b"),
+                    new Option<string>("--two").FromAmong("two-a", "two-b")
                 });
 
             var commandLine = "outer --two";
@@ -591,7 +587,7 @@ public void Completions_can_be_provided_in_the_absence_of_validation()
         {
             var command = new Command("the-command")
                 {
-                    new Option("-t", arity: ArgumentArity.ExactlyOne)
+                    new Option<string>("-t")
                         .AddCompletions("vegetable", "mineral", "animal")
                 };
 
@@ -615,9 +611,8 @@ public void Command_argument_completions_can_be_provided_using_a_delegate()
             {
                 new Command("one")
                 {
-                    new Argument
+                    new Argument<string>
                         {
-                            Arity = ArgumentArity.ExactlyOne,
                             Completions = { _ => new[] { "vegetable", "mineral", "animal" } }
                         }
                 }
@@ -653,11 +648,11 @@ public void When_caller_does_the_tokenizing_then_argument_completions_are_based_
         {
             var command = new Command("outer")
             {
-                new Option("one", arity: ArgumentArity.ExactlyOne)
+                new Option<string>("one")
                     .FromAmong("one-a", "one-b", "one-c"),
-                new Option("two", arity: ArgumentArity.ExactlyOne)
+                new Option<string>("two")
                     .FromAmong("two-a", "two-b", "two-c"),
-                new Option("three", arity: ArgumentArity.ExactlyOne)
+                new Option<string>("three")
                     .FromAmong("three-a", "three-b", "three-c")
             };
 
@@ -680,11 +675,11 @@ public void When_parsing_from_array_then_argument_completions_are_based_on_the_p
         {
             var command = new Command("outer")
             {
-                new Option("one", arity: ArgumentArity.ExactlyOne)
+                new Option<string>("one")
                     .FromAmong("one-a", "one-b", "one-c"),
-                new Option("two", arity: ArgumentArity.ExactlyOne)
+                new Option<string>("two")
                     .FromAmong("two-a", "two-b", "two-c"),
-                new Option("three", arity: ArgumentArity.ExactlyOne)
+                new Option<string>("three")
                     .FromAmong("three-a", "three-b", "three-c")
             };
 
@@ -703,24 +698,15 @@ public void When_parsing_from_text_then_argument_completions_are_based_on_the_pr
             {
                 new Command("one")
                 {
-                    new Argument
-                    {
-                        Arity = ArgumentArity.ExactlyOne
-                    }.FromAmong("one-a", "one-b", "one-c")
+                    new Argument<string>().FromAmong("one-a", "one-b", "one-c")
                 },
                 new Command("two")
                 {
-                    new Argument
-                    {
-                        Arity = ArgumentArity.ExactlyOne
-                    }.FromAmong("two-a", "two-b", "two-c")
+                    new Argument<string>().FromAmong("two-a", "two-b", "two-c")
                 },
                 new Command("three")
                 {
-                    new Argument
-                    {
-                        Arity = ArgumentArity.ExactlyOne
-                    }.FromAmong("three-a", "three-b", "three-c")
+                    new Argument<string>().FromAmong("three-a", "three-b", "three-c")
                 }
             };
 
@@ -739,24 +725,15 @@ public void When_parsing_from_array_then_argument_completions_are_based_on_the_p
             {
                 new Command("one")
                 {
-                    new Argument
-                    {
-                        Arity = ArgumentArity.ExactlyOne
-                    }.FromAmong("one-a", "one-b", "one-c")
+                    new Argument<string>().FromAmong("one-a", "one-b", "one-c")
                 },
                 new Command("two")
                 {
-                    new Argument
-                    {
-                        Arity = ArgumentArity.ExactlyOne
-                    }.FromAmong("two-a", "two-b", "two-c")
+                    new Argument<string>().FromAmong("two-a", "two-b", "two-c")
                 },
                 new Command("three")
                 {
-                    new Argument
-                    {
-                        Arity = ArgumentArity.ExactlyOne
-                    }.FromAmong("three-a", "three-b", "three-c")
+                    new Argument<string>().FromAmong("three-a", "three-b", "three-c")
                 }
             };
 
diff --git a/src/System.CommandLine.Tests/Invocation/TypoCorrectionTests.cs b/src/System.CommandLine.Tests/Invocation/TypoCorrectionTests.cs
index aa1dc1f382..8223feb1b7 100644
--- a/src/System.CommandLine.Tests/Invocation/TypoCorrectionTests.cs
+++ b/src/System.CommandLine.Tests/Invocation/TypoCorrectionTests.cs
@@ -15,7 +15,7 @@ public class TypoCorrectionTests
         [Fact]
         public async Task When_option_is_mistyped_it_is_suggested()
         {
-            var option = new Option("info");
+            var option = new Option<string>("info");
 
             var parser =
                 new CommandLineBuilder(new RootCommand
@@ -35,7 +35,7 @@ public async Task When_option_is_mistyped_it_is_suggested()
         [Fact]
         public async Task When_there_are_no_matches_then_nothing_is_suggested()
         {
-            var option = new Option("info");
+            var option = new Option<bool>("info");
 
             var parser =
                 new CommandLineBuilder(new RootCommand
@@ -77,8 +77,8 @@ public async Task When_there_are_multiple_matches_it_picks_the_best_matches()
         {
             var fromCommand = new Command("from");
             var seenCommand = new Command("seen");
-            var aOption = new Option("a");
-            var beenOption = new Option("been");
+            var aOption = new Option<bool>("a");
+            var beenOption = new Option<bool>("been");
             var parser =
                 new CommandLineBuilder(new RootCommand
                     {
@@ -146,9 +146,9 @@ public async Task Arguments_are_not_suggested()
         [Fact]
         public async Task Hidden_options_are_not_suggested()
         {
-            var fromOption = new Option("from");
-            var seenOption = new Option("seen") { IsHidden = true };
-            var beenOption = new Option("been");
+            var fromOption = new Option<string>("from");
+            var seenOption = new Option<string>("seen") { IsHidden = true };
+            var beenOption = new Option<string>("been");
 
             var parser =
                 new CommandLineBuilder(new RootCommand
@@ -172,8 +172,8 @@ public async Task Suggestions_favor_matches_with_prefix()
             var parser =
                 new CommandLineBuilder(new RootCommand
                     {
-                        new Option(new[] { "/call", "-call", "--call" }),
-                        new Option(new[] { "/email", "-email", "--email" })
+                        new Option<string>(new[] { "/call", "-call", "--call" }),
+                        new Option<string>(new[] { "/email", "-email", "--email" })
                     })
                     .UseTypoCorrections()
                     .Build();
diff --git a/src/System.CommandLine.Tests/OptionTests.cs b/src/System.CommandLine.Tests/OptionTests.cs
index 626b93e897..7d87ebc5f3 100644
--- a/src/System.CommandLine.Tests/OptionTests.cs
+++ b/src/System.CommandLine.Tests/OptionTests.cs
@@ -22,7 +22,7 @@ public void When_an_option_has_only_one_alias_then_that_alias_is_its_name()
         [Fact]
         public void When_an_option_has_several_aliases_then_the_longest_alias_is_its_name()
         {
-            var option = new Option(new[] { "myname", "m" });
+            var option = new Option<string>(new[] { "myname", "m" });
 
             option.Name.Should().Be("myname");
         }
@@ -30,7 +30,7 @@ public void When_an_option_has_several_aliases_then_the_longest_alias_is_its_nam
         [Fact]
         public void Option_names_do_not_contain_prefix_characters()
         {
-            var option = new Option(new[] { "--myname", "m" });
+            var option = new Option<string>(new[] { "--myname", "m" });
 
             option.Name.Should().Be("myname");
         }
@@ -38,7 +38,7 @@ public void Option_names_do_not_contain_prefix_characters()
         [Fact]
         public void Aliases_is_aware_of_added_alias()
         {
-            var option = new Option("--original");
+            var option = new Option<string>("--original");
 
             option.AddAlias("--added");
 
@@ -49,7 +49,7 @@ public void Aliases_is_aware_of_added_alias()
         [Fact]
         public void RawAliases_is_aware_of_added_alias()
         {
-            var option = new Option("--original");
+            var option = new Option<string>("--original");
 
             option.AddAlias("--added");
 
@@ -60,7 +60,7 @@ public void RawAliases_is_aware_of_added_alias()
         [Fact]
         public void A_prefixed_alias_can_be_added_to_an_option()
         {
-            var option = new Option("--apple");
+            var option = new Option<string>("--apple");
 
             option.AddAlias("-a");
 
@@ -71,7 +71,7 @@ public void A_prefixed_alias_can_be_added_to_an_option()
         [Fact]
         public void Option_aliases_are_case_sensitive()
         {
-            var option = new Option(new[] { "-o" });
+            var option = new Option<string>(new[] { "-o" });
 
             option.HasAlias("O").Should().BeFalse();
         }
@@ -79,7 +79,7 @@ public void Option_aliases_are_case_sensitive()
         [Fact]
         public void HasAlias_accepts_prefixed_short_value()
         {
-            var option = new Option(new[] { "-o", "--option" });
+            var option = new Option<string>(new[] { "-o", "--option" });
 
             option.HasAlias("-o").Should().BeTrue();
         }
@@ -87,7 +87,7 @@ public void HasAlias_accepts_prefixed_short_value()
         [Fact]
         public void HasAliasIgnorePrefix_accepts_unprefixed_short_value()
         {
-            var option = new Option(new[] { "-o", "--option" });
+            var option = new Option<string>(new[] { "-o", "--option" });
 
             option.HasAliasIgnoringPrefix("o").Should().BeTrue();
         }
@@ -95,7 +95,7 @@ public void HasAliasIgnorePrefix_accepts_unprefixed_short_value()
         [Fact]
         public void HasAlias_accepts_prefixed_long_value()
         {
-            var option = new Option(new[] { "-o", "--option" });
+            var option = new Option<string>(new[] { "-o", "--option" });
 
             option.HasAlias("--option").Should().BeTrue();
         }
@@ -103,7 +103,7 @@ public void HasAlias_accepts_prefixed_long_value()
         [Fact]
         public void HasAliasIgnorePrefix_accepts_unprefixed_long_value()
         {
-            var option = new Option(new[] { "-o", "--option" });
+            var option = new Option<string>(new[] { "-o", "--option" });
 
             option.HasAliasIgnoringPrefix("option").Should().BeTrue();
         }
@@ -111,7 +111,7 @@ public void HasAliasIgnorePrefix_accepts_unprefixed_long_value()
         [Fact]
         public void It_is_not_necessary_to_specify_a_prefix_when_adding_an_option()
         {
-            var option = new Option(new[] { "o" });
+            var option = new Option<string>(new[] { "o" });
 
             option.HasAlias("o").Should().BeTrue();
         }
@@ -119,7 +119,7 @@ public void It_is_not_necessary_to_specify_a_prefix_when_adding_an_option()
         [Fact]
         public void An_option_must_have_at_least_one_alias()
         {
-            Action create = () => new Option(Array.Empty<string>());
+            Action create = () => new Option<string>(Array.Empty<string>());
 
             create.Should()
                   .Throw<ArgumentException>()
@@ -132,7 +132,7 @@ public void An_option_must_have_at_least_one_alias()
         [Fact]
         public void An_option_cannot_have_an_empty_alias()
         {
-            Action create = () => new Option(new[] { "" });
+            Action create = () => new Option<string>(new[] { "" });
 
             create.Should()
                   .Throw<ArgumentException>()
@@ -145,7 +145,7 @@ public void An_option_cannot_have_an_empty_alias()
         [Fact]
         public void An_option_cannot_have_an_alias_consisting_entirely_of_whitespace()
         {
-            Action create = () => new Option(new[] { "  \t" });
+            Action create = () => new Option<string>(new[] { "  \t" });
 
             create.Should()
                   .Throw<ArgumentException>()
@@ -158,7 +158,7 @@ public void An_option_cannot_have_an_alias_consisting_entirely_of_whitespace()
         [Fact]
         public void Raw_aliases_are_exposed_by_an_option()
         {
-            var option = new Option(new[] { "-h", "--help", "/?" });
+            var option = new Option<string>(new[] { "-h", "--help", "/?" });
 
             option.Aliases
                   .Should()
@@ -179,17 +179,16 @@ public void When_an_option_is_created_with_an_alias_that_contains_whitespace_the
                   .Which
                   .Message
                   .Should()
-                  .Contain($"Option alias cannot contain whitespace: \"{alias}\"");
+                  .Contain($"Alias cannot contain whitespace: \"{alias}\"");
         }
 
         [Theory]
         [InlineData("-x ")]
         [InlineData(" -x")]
         [InlineData("--aa aa")]
-        public void When_an_option_alias_is_added_and_contains_whitespace_then_an_informative_error_is_returned(
-            string alias)
+        public void When_an_option_alias_is_added_and_contains_whitespace_then_an_informative_error_is_returned(string alias)
         {
-            var option = new Option("-x");
+            var option = new Option<bool>("-x");
 
             Action addAlias = () => option.AddAlias(alias);
 
@@ -198,7 +197,7 @@ public void When_an_option_alias_is_added_and_contains_whitespace_then_an_inform
                     .Which
                     .Message
                     .Should()
-                    .Contain($"Option alias cannot contain whitespace: \"{alias}\"");
+                    .Contain($"Alias cannot contain whitespace: \"{alias}\"");
         }
 
         [Theory]
@@ -208,7 +207,7 @@ public void When_an_option_alias_is_added_and_contains_whitespace_then_an_inform
         public void When_options_use_different_prefixes_they_still_work(string prefix)
         {
             var optionA = new Option<string>(prefix + "a");
-            var optionB = new Option(prefix + "b");
+            var optionB = new Option<string>(prefix + "b");
             var optionC = new Option<string>(prefix + "c");
 
             var rootCommand = new RootCommand
@@ -228,7 +227,7 @@ public void When_options_use_different_prefixes_they_still_work(string prefix)
         [Fact]
         public void When_option_not_explicitly_provides_help_will_use_default_help()
         {
-            var option = new Option(new[] { "-o", "--option" }, "desc");
+            var option = new Option<string>(new[] { "-o", "--option" }, "desc");
 
             option.Name.Should().Be("option");
             option.Description.Should().Be("desc");
@@ -238,7 +237,7 @@ public void When_option_not_explicitly_provides_help_will_use_default_help()
         [Fact]
         public void Argument_takes_option_alias_as_its_name_when_it_is_not_provided()
         {
-            var command = new Option("--alias", arity: ArgumentArity.ZeroOrOne);
+            var command = new Option<string>("--alias");
 
             command.Name.Should().Be("alias");
         }
@@ -246,7 +245,7 @@ public void Argument_takes_option_alias_as_its_name_when_it_is_not_provided()
         [Fact]
         public void Argument_retains_name_when_it_is_provided()
         {
-            var option = new Option("-alias", arity: ArgumentArity.ZeroOrOne)
+            var option = new Option<string>("-alias")
             {
                 ArgumentHelpName = "arg"
             };
@@ -336,7 +335,7 @@ public void Option_of_string_defaults_to_null_when_not_specified()
         [Fact]
         public void When_Name_is_set_to_its_current_value_then_it_is_not_removed_from_aliases()
         {
-            var option = new Option("--name");
+            var option = new Option<string>("--name");
 
             option.Name = "name";
 
@@ -372,23 +371,7 @@ public void Option_of_boolean_defaults_to_false_when_not_specified()
                 .Should()
                 .BeFalse();
         }
-
-        [Fact]
-        public void Arity_of_non_generic_option_defaults_to_zero()
-        {
-            var option = new Option("-x");
-
-            option.Arity.Should().BeEquivalentTo(ArgumentArity.Zero);
-        }
-
-        [Fact]
-        public void ArgumentType_of_non_generic_option_defaults_to_bool()
-        {
-            var option = new Option("-x");
-
-            option.ValueType.Should().Be(typeof(bool));
-        }
-
+        
         protected override Symbol CreateSymbol(string name) => new Option(name);
     }
 }
diff --git a/src/System.CommandLine.Tests/ParseDiagramTests.cs b/src/System.CommandLine.Tests/ParseDiagramTests.cs
index 3c2acd4e6f..e1cfd8bf45 100644
--- a/src/System.CommandLine.Tests/ParseDiagramTests.cs
+++ b/src/System.CommandLine.Tests/ParseDiagramTests.cs
@@ -16,14 +16,11 @@ public void Parse_result_diagram_helps_explain_parse_operation()
             var parser = new Parser(
                 new Command(
                     "the-command")
-                  {
-                        new Option("-x", arity: ArgumentArity.ExactlyOne),
-                        new Option("-y"),
-                        new Argument
-                        {
-                            Arity = ArgumentArity.ZeroOrMore
-                        }
-                    });
+                {
+                    new Option<string>("-x"),
+                    new Option<bool>("-y"),
+                    new Argument<string[]>()
+                });
 
             var result = parser.Parse("the-command -x one -y two three");
 
diff --git a/src/System.CommandLine/IdentifierSymbol.cs b/src/System.CommandLine/IdentifierSymbol.cs
index 6230e7a60d..92b49598a2 100644
--- a/src/System.CommandLine/IdentifierSymbol.cs
+++ b/src/System.CommandLine/IdentifierSymbol.cs
@@ -91,7 +91,7 @@ private void ThrowIfAliasIsInvalid(string alias)
             {
                 if (char.IsWhiteSpace(alias[i]))
                 {
-                    throw new ArgumentException($"{GetType().Name} alias cannot contain whitespace: \"{alias}\"", nameof(alias));
+                    throw new ArgumentException($"Alias cannot contain whitespace: \"{alias}\"", nameof(alias));
                 }
             }
         }
diff --git a/src/System.CommandLine/Parsing/ParseResultExtensions.cs b/src/System.CommandLine/Parsing/ParseResultExtensions.cs
index db990bfb39..0f233fe4f7 100644
--- a/src/System.CommandLine/Parsing/ParseResultExtensions.cs
+++ b/src/System.CommandLine/Parsing/ParseResultExtensions.cs
@@ -80,90 +80,99 @@ private static void Diagram(
                 builder.Append("!");
             }
 
-            if (symbolResult is OptionResult optionResult &&
-                optionResult.IsImplicit)
-            {
-                builder.Append("*");
-            }
 
-            if (symbolResult is ArgumentResult argumentResult)
+            switch (symbolResult)
             {
-                var includeArgumentName =
-                    argumentResult.Argument.FirstParent!.Symbol is Command command &&
-                    command.Arguments.Count > 1;
-
-                if (includeArgumentName)
+                case ArgumentResult argumentResult:
                 {
-                    builder.Append("[ ");
-                    builder.Append(argumentResult.Argument.Name);
-                    builder.Append(" ");
-                }
+                    var includeArgumentName =
+                        argumentResult.Argument.FirstParent!.Symbol is Command command &&
+                        command.Arguments.Count > 1;
 
-                if (argumentResult.Argument.Arity.MaximumNumberOfValues > 0)
-                {
-                    ArgumentConversionResult conversionResult = argumentResult.GetArgumentConversionResult();
-                    switch (conversionResult.Result)
+                    if (includeArgumentName)
+                    {
+                        builder.Append("[ ");
+                        builder.Append(argumentResult.Argument.Name);
+                        builder.Append(" ");
+                    }
+
+                    if (argumentResult.Argument.Arity.MaximumNumberOfValues > 0)
                     {
-                        case ArgumentConversionResultType.NoArgument:
-                            break;
-                        case ArgumentConversionResultType.Successful:
-                            switch (conversionResult.Value)
-                            {
-                                case string s:
-                                    builder.Append($"<{s}>");
-                                    break;
+                        ArgumentConversionResult conversionResult = argumentResult.GetArgumentConversionResult();
+                        switch (conversionResult.Result)
+                        {
+                            case ArgumentConversionResultType.NoArgument:
+                                break;
+                            case ArgumentConversionResultType.Successful:
+                                switch (conversionResult.Value)
+                                {
+                                    case string s:
+                                        builder.Append($"<{s}>");
+                                        break;
                                 
-                                case IEnumerable items:
-                                    builder.Append("<");
-                                    builder.Append(
-                                        string.Join("> <",
-                                                    items.Cast<object>().ToArray()));
-                                    builder.Append(">");
-                                    break;
-
-                                default:
-                                    builder.Append("<");
-                                    builder.Append(conversionResult.Value);
-                                    builder.Append(">");
-                                    break;
-                            }
-
-                            break;
-
-                        default: // failures
-                            builder.Append("<");
-                            builder.Append(string.Join("> <", symbolResult.Tokens.Select(t => t.Value)));
-                            builder.Append(">");
-
-                            break;
+                                    case IEnumerable items:
+                                        builder.Append("<");
+                                        builder.Append(
+                                            string.Join("> <",
+                                                        items.Cast<object>().ToArray()));
+                                        builder.Append(">");
+                                        break;
+
+                                    default:
+                                        builder.Append("<");
+                                        builder.Append(conversionResult.Value);
+                                        builder.Append(">");
+                                        break;
+                                }
+
+                                break;
+
+                            default: // failures
+                                builder.Append("<");
+                                builder.Append(string.Join("> <", symbolResult.Tokens.Select(t => t.Value)));
+                                builder.Append(">");
+
+                                break;
+                        }
                     }
-                }
 
-                if (includeArgumentName)
-                {
-                    builder.Append(" ]");
+                    if (includeArgumentName)
+                    {
+                        builder.Append(" ]");
+                    }
+
+                    break;
                 }
-            }
-            else
-            {
-                builder.Append("[ ");
-                builder.Append(symbolResult.Token().Value);
 
-                for (var i = 0; i < symbolResult.Children.Count; i++)
+                default:
                 {
-                    var child = symbolResult.Children[i];
+                    if (symbolResult is OptionResult { IsImplicit: true })
+                    {
+                        builder.Append("*");
+                    }
+
+                    builder.Append("[ ");
+                    builder.Append(symbolResult.Token().Value);
 
-                    if (child is ArgumentResult arg && 
-                        arg.Argument.Arity.MaximumNumberOfValues == 0)
+                    for (var i = 0; i < symbolResult.Children.Count; i++)
                     {
-                        continue;
+                        var child = symbolResult.Children[i];
+
+                        if (child is ArgumentResult arg &&
+                            (arg.Argument.ValueType == typeof(bool) ||
+                             arg.Argument.Arity.MaximumNumberOfValues == 0))
+                        {
+                            continue;
+                        }
+
+                        builder.Append(" ");
+
+                        builder.Diagram(child, parseResult);
                     }
 
-                    builder.Append(" ");
-                    builder.Diagram(child, parseResult);
+                    builder.Append(" ]");
+                    break;
                 }
-
-                builder.Append(" ]");
             }
         }
 

From 863c95aa5df91d45cf9bed480d881a1ed9c196fc Mon Sep 17 00:00:00 2001
From: Jon Sequeira <jonsequeira@gmail.com>
Date: Mon, 14 Mar 2022 16:12:20 -0700
Subject: [PATCH 04/11] wip

---
 ...ommandLine_api_is_not_changed.approved.txt |  1 +
 .../CommandLine.cs                            |  5 ++-
 .../ModelBinderTests.cs                       |  5 +--
 ...indingCommandHandlerTests.BindingByName.cs |  6 ++--
 .../ModelBindingCommandHandlerTests.cs        |  3 +-
 ...ndLine.NamingConventionBinder.Tests.csproj |  2 ++
 .../Binding/TypeConversionTests.cs            |  2 +-
 src/System.CommandLine.Tests/CommandTests.cs  |  3 +-
 .../CompletionTests.cs                        |  2 +-
 .../ParsingValidationTests.cs                 |  8 ++---
 .../Utility/OptionBuilder.cs                  | 32 +++++++++++++++++++
 src/System.CommandLine/Option.cs              |  8 -----
 12 files changed, 54 insertions(+), 23 deletions(-)
 create mode 100644 src/System.CommandLine.Tests/Utility/OptionBuilder.cs

diff --git a/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt b/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
index 7cd496d848..6ffedb9684 100644
--- a/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
+++ b/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
@@ -182,6 +182,7 @@
     public System.String VersionOptionCannotBeCombinedWithOtherArguments(System.String optionAlias)
     public System.String VersionOptionDescription()
   public class Option : IdentifierSymbol, System.CommandLine.Binding.IValueDescriptor, System.CommandLine.Completions.ICompletionSource
+    .ctor(System.String name)
     .ctor(System.String name, System.String description = null, System.Type argumentType = null, System.Func<System.Object> getDefaultValue = null, ArgumentArity arity = null)
     .ctor(System.String[] aliases, System.String description = null, System.Type argumentType = null, System.Func<System.Object> getDefaultValue = null, ArgumentArity arity = null)
     public System.Boolean AllowMultipleArgumentsPerToken { get; set; }
diff --git a/src/System.CommandLine.DragonFruit/CommandLine.cs b/src/System.CommandLine.DragonFruit/CommandLine.cs
index c5e64061e5..f08938f5ff 100644
--- a/src/System.CommandLine.DragonFruit/CommandLine.cs
+++ b/src/System.CommandLine.DragonFruit/CommandLine.cs
@@ -296,11 +296,14 @@ public static Option BuildOption(this ParameterDescriptor parameter)
             {
                 getDefaultValue = parameter.GetDefaultValue;
             }
-            return new Option(
+
+            var option = new Option(
                 parameter.BuildAlias(),
                 parameter.ValueName,
                 parameter.ValueType,
                 getDefaultValue);
+
+            return option;
         }
 
         private static string GetDefaultXmlDocsFileLocation(Assembly assembly)
diff --git a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBinderTests.cs b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBinderTests.cs
index 23bf594765..fd4a071b63 100644
--- a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBinderTests.cs
+++ b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBinderTests.cs
@@ -6,6 +6,7 @@
 using System.CommandLine.Invocation;
 using System.CommandLine.Parsing;
 using System.CommandLine.Tests.Binding;
+using System.CommandLine.Utility;
 using System.IO;
 using System.Threading.Tasks;
 using FluentAssertions;
@@ -30,7 +31,7 @@ public void Option_arguments_are_bound_by_name_to_constructor_parameters(
 
         var command = new Command("the-command")
         {
-            new Option("--value", argumentType: type)
+            OptionBuilder.CreateOption("--value", type)
         };
 
         var bindingContext = new InvocationContext(command.Parse(commandLine)).BindingContext;
@@ -135,7 +136,7 @@ public void Option_arguments_are_bound_by_name_to_property_setters(
 
         var command = new Command("the-command")
         {
-            new Option("--value", argumentType: type)
+            OptionBuilder.CreateOption("--value", type)
         };
         var parser = new Parser(command);
 
diff --git a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.BindingByName.cs b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.BindingByName.cs
index 130fd9b45d..156cd99b4a 100644
--- a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.BindingByName.cs
+++ b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.BindingByName.cs
@@ -1,10 +1,10 @@
 // // Copyright (c) .NET Foundation and contributors. All rights reserved.
 // // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
-using System.CommandLine.Binding;
 using System.CommandLine.Invocation;
 using System.CommandLine.IO;
 using System.CommandLine.Tests.Binding;
+using System.CommandLine.Utility;
 using System.IO;
 using System.Threading.Tasks;
 using FluentAssertions;
@@ -35,7 +35,7 @@ public async Task Option_arguments_are_bound_by_name_to_method_parameters(
 
             var command = new Command("the-command")
             {
-                new Option("--value", argumentType: type)
+                OptionBuilder.CreateOption("--value", type)
             };
 
             var console = new TestConsole();
@@ -99,7 +99,7 @@ public async Task Option_arguments_are_bound_by_name_to_the_constructor_paramete
 
             var command = new Command("the-command")
             {
-                new Option("--value", argumentType: type)
+                OptionBuilder.CreateOption("--value", type)
             };
 
             var console = new TestConsole();
diff --git a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs
index 9c715838a0..97d12d9838 100644
--- a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs
+++ b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs
@@ -5,6 +5,7 @@
 using System.CommandLine.Invocation;
 using System.CommandLine.IO;
 using System.CommandLine.Tests.Binding;
+using System.CommandLine.Utility;
 using System.IO;
 using System.Linq;
 using System.Reflection;
@@ -283,7 +284,7 @@ public async Task Handler_method_receive_option_arguments_explicitly_bound_to_th
 
         var handler = CommandHandler.Create(captureMethod);
 
-        var option = new Option("--value", argumentType: testCase.ParameterType);
+        var option = OptionBuilder.CreateOption("--value", testCase.ParameterType);
 
         var command = new Command("command")
         {
diff --git a/src/System.CommandLine.NamingConventionBinder.Tests/System.CommandLine.NamingConventionBinder.Tests.csproj b/src/System.CommandLine.NamingConventionBinder.Tests/System.CommandLine.NamingConventionBinder.Tests.csproj
index b86154e044..4b89820ac3 100644
--- a/src/System.CommandLine.NamingConventionBinder.Tests/System.CommandLine.NamingConventionBinder.Tests.csproj
+++ b/src/System.CommandLine.NamingConventionBinder.Tests/System.CommandLine.NamingConventionBinder.Tests.csproj
@@ -12,10 +12,12 @@
     <EmbeddedResource Remove="TestResults\**" />
     <None Remove="TestResults\**" />
   </ItemGroup>
+
   <ItemGroup>
     <Compile Include="..\System.CommandLine.Tests\Binding\TestModels.cs" Link="TestModels.cs" />
     <Compile Include="..\System.CommandLine.Tests\Utility\AssertionExtensions.cs" Link="Utility\AssertionExtensions.cs" />
     <Compile Include="..\System.CommandLine.Tests\Utility\ConsoleAssertions.cs" Link="Utility\ConsoleAssertions.cs" />
+    <Compile Include="..\System.CommandLine.Tests\Utility\OptionBuilder.cs" Link="Utility\OptionBuilder.cs" />
   </ItemGroup>
   
   <ItemGroup>
diff --git a/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs b/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
index d37eccf161..434a2b2a41 100644
--- a/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
+++ b/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
@@ -239,7 +239,7 @@ public void Generic_option_bool_parses_when_passed_to_non_generic_GetValueForOpt
         [Fact]
         public void When_exactly_one_argument_is_expected_and_none_are_provided_then_getting_value_throws()
         {
-            var option = new Option("-x", arity: ArgumentArity.ExactlyOne);
+            var option = new Option<string>("-x");
 
             var command = new Command("the-command")
             {
diff --git a/src/System.CommandLine.Tests/CommandTests.cs b/src/System.CommandLine.Tests/CommandTests.cs
index 32858bb53e..28b3df6c71 100644
--- a/src/System.CommandLine.Tests/CommandTests.cs
+++ b/src/System.CommandLine.Tests/CommandTests.cs
@@ -2,7 +2,6 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using FluentAssertions;
-using System.Collections.Generic;
 using System.CommandLine.Parsing;
 using System.Linq;
 using Xunit;
@@ -20,7 +19,7 @@ public CommandTests()
                 {
                     new Command("inner")
                     {
-                        new Option("--option", arity: ArgumentArity.ExactlyOne)
+                        new Option<string>("--option")
                     }
                 });
         }
diff --git a/src/System.CommandLine.Tests/CompletionTests.cs b/src/System.CommandLine.Tests/CompletionTests.cs
index 9ad79f32df..ddd85995e5 100644
--- a/src/System.CommandLine.Tests/CompletionTests.cs
+++ b/src/System.CommandLine.Tests/CompletionTests.cs
@@ -25,7 +25,7 @@ public CompletionTests(ITestOutputHelper output)
         [Fact]
         public void Option_GetCompletions_returns_argument_completions_if_configured()
         {
-            var option = new Option("--hello", arity: ArgumentArity.ExactlyOne)
+            var option = new Option<string>("--hello")
                 .AddCompletions("one", "two", "three");
 
             var completions = option.GetCompletions();
diff --git a/src/System.CommandLine.Tests/ParsingValidationTests.cs b/src/System.CommandLine.Tests/ParsingValidationTests.cs
index f100da3281..555ce97caf 100644
--- a/src/System.CommandLine.Tests/ParsingValidationTests.cs
+++ b/src/System.CommandLine.Tests/ParsingValidationTests.cs
@@ -24,7 +24,7 @@ public ParsingValidationTests(ITestOutputHelper output)
         [Fact]
         public void When_an_option_accepts_only_specific_arguments_but_a_wrong_one_is_supplied_then_an_informative_error_is_returned()
         {
-            var option = new Option("-x", arity: ArgumentArity.ExactlyOne)
+            var option = new Option<string>("-x")
                 .FromAmong("this", "that", "the-other-thing");
 
             var result = option.Parse("-x none-of-those");
@@ -40,7 +40,7 @@ public void When_an_option_accepts_only_specific_arguments_but_a_wrong_one_is_su
         [Fact]
         public void When_an_option_has_en_error_then_the_error_has_a_reference_to_the_option()
         {
-            var option = new Option("-x", arity: ArgumentArity.ExactlyOne)
+            var option = new Option<string>("-x")
                 .FromAmong("this", "that");
 
             var result = option.Parse("-x something_else");
@@ -142,7 +142,7 @@ public void When_FromAmong_is_used_for_multiple_arguments_and_invalid_input_is_p
         [Fact]
         public void When_a_required_argument_is_not_supplied_then_an_error_is_returned()
         {
-            var option = new Option("-x", arity: ArgumentArity.ExactlyOne);
+            var option = new Option<string>("-x");
 
             var result = option.Parse("-x");
 
@@ -848,7 +848,7 @@ public void A_command_argument_with_multiple_FileSystemInfos_can_be_invalid_base
                     {
                         Arity = ArgumentArity.ZeroOrMore
                     }.ExistingOnly(),
-                    new Option("--to", arity: ArgumentArity.ExactlyOne)
+                    new Option<string>("--to")
                 };
 
                 var path = NonexistentPath();
diff --git a/src/System.CommandLine.Tests/Utility/OptionBuilder.cs b/src/System.CommandLine.Tests/Utility/OptionBuilder.cs
new file mode 100644
index 0000000000..d09b2eea60
--- /dev/null
+++ b/src/System.CommandLine.Tests/Utility/OptionBuilder.cs
@@ -0,0 +1,32 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System.Reflection;
+
+namespace System.CommandLine.Utility
+{
+    internal static class OptionBuilder
+    {
+        private static readonly ConstructorInfo _ctor;
+
+        static OptionBuilder()
+        {
+            _ctor = typeof(Option<string>).GetConstructor(new[] { typeof(string), typeof(string) });
+        }
+
+        public static Option CreateOption(string name, Type valueType)
+        {
+            var optionType = typeof(Option<>).MakeGenericType(valueType);
+
+#if NET6_0_OR_GREATER
+            var ctor = (ConstructorInfo)optionType.GetMemberWithSameMetadataDefinitionAs(_ctor);
+#else
+            var ctor = optionType.GetConstructor(new[] { typeof(string), typeof(string) });
+#endif
+
+            var option = (Option)ctor.Invoke(new object[] { name, null });
+
+            return option;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/System.CommandLine/Option.cs b/src/System.CommandLine/Option.cs
index 8d82d528b4..27a3d2cff3 100644
--- a/src/System.CommandLine/Option.cs
+++ b/src/System.CommandLine/Option.cs
@@ -25,14 +25,6 @@ public Option(string name) : this(name, description: null)
         {
         }
 
-        public Option(string name, ArgumentArity arity) : this(name, description: null, arity: arity)
-        {
-        }
-
-        public Option(string name, Func<object?>? getDefaultValue) : this(name,null, getDefaultValue: getDefaultValue)
-        {
-        }
-
         /// <summary>
         /// Initializes a new instance of the <see cref="Option"/> class.
         /// </summary>

From b150c2d96de95771940a46e4b6eab891cd8e529f Mon Sep 17 00:00:00 2001
From: Jon Sequeira <jonsequeira@gmail.com>
Date: Mon, 14 Mar 2022 16:30:52 -0700
Subject: [PATCH 05/11] wip

---
 .../Utility => Common}/OptionBuilder.cs            |  0
 src/System.CommandLine.DragonFruit/CommandLine.cs  | 14 +++++++++-----
 .../System.CommandLine.DragonFruit.csproj          |  4 ++++
 ...CommandLine.NamingConventionBinder.Tests.csproj |  2 +-
 4 files changed, 14 insertions(+), 6 deletions(-)
 rename src/{System.CommandLine.Tests/Utility => Common}/OptionBuilder.cs (100%)

diff --git a/src/System.CommandLine.Tests/Utility/OptionBuilder.cs b/src/Common/OptionBuilder.cs
similarity index 100%
rename from src/System.CommandLine.Tests/Utility/OptionBuilder.cs
rename to src/Common/OptionBuilder.cs
diff --git a/src/System.CommandLine.DragonFruit/CommandLine.cs b/src/System.CommandLine.DragonFruit/CommandLine.cs
index f08938f5ff..f8996f0a71 100644
--- a/src/System.CommandLine.DragonFruit/CommandLine.cs
+++ b/src/System.CommandLine.DragonFruit/CommandLine.cs
@@ -8,6 +8,7 @@
 using System.CommandLine.NamingConventionBinder;
 using System.CommandLine.Parsing;
 using System.CommandLine.Rendering;
+using System.CommandLine.Utility;
 using System.IO;
 using System.Linq;
 using System.Reflection;
@@ -297,11 +298,14 @@ public static Option BuildOption(this ParameterDescriptor parameter)
                 getDefaultValue = parameter.GetDefaultValue;
             }
 
-            var option = new Option(
-                parameter.BuildAlias(),
-                parameter.ValueName,
-                parameter.ValueType,
-                getDefaultValue);
+            var option = OptionBuilder.CreateOption(parameter.BuildAlias(), parameter.ValueType);
+            
+            option.Description = parameter.ValueName;
+
+            if (getDefaultValue is not null)
+            {
+                option.SetDefaultValueFactory(getDefaultValue);
+            }
 
             return option;
         }
diff --git a/src/System.CommandLine.DragonFruit/System.CommandLine.DragonFruit.csproj b/src/System.CommandLine.DragonFruit/System.CommandLine.DragonFruit.csproj
index e566bfd10d..e67b723ecb 100644
--- a/src/System.CommandLine.DragonFruit/System.CommandLine.DragonFruit.csproj
+++ b/src/System.CommandLine.DragonFruit/System.CommandLine.DragonFruit.csproj
@@ -12,4 +12,8 @@
     <ProjectReference Include="..\System.CommandLine.NamingConventionBinder\System.CommandLine.NamingConventionBinder.csproj" />
     <Content Include="targets/*" PackagePath="build/$(TargetFramework)/" />
   </ItemGroup>
+
+  <ItemGroup>
+    <Compile Include="..\Common\OptionBuilder.cs" Link="Utility\OptionBuilder.cs" />
+  </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/System.CommandLine.NamingConventionBinder.Tests/System.CommandLine.NamingConventionBinder.Tests.csproj b/src/System.CommandLine.NamingConventionBinder.Tests/System.CommandLine.NamingConventionBinder.Tests.csproj
index 4b89820ac3..96276ec493 100644
--- a/src/System.CommandLine.NamingConventionBinder.Tests/System.CommandLine.NamingConventionBinder.Tests.csproj
+++ b/src/System.CommandLine.NamingConventionBinder.Tests/System.CommandLine.NamingConventionBinder.Tests.csproj
@@ -14,10 +14,10 @@
   </ItemGroup>
 
   <ItemGroup>
+    <Compile Include="..\Common\OptionBuilder.cs" Link="Utility\OptionBuilder.cs" />
     <Compile Include="..\System.CommandLine.Tests\Binding\TestModels.cs" Link="TestModels.cs" />
     <Compile Include="..\System.CommandLine.Tests\Utility\AssertionExtensions.cs" Link="Utility\AssertionExtensions.cs" />
     <Compile Include="..\System.CommandLine.Tests\Utility\ConsoleAssertions.cs" Link="Utility\ConsoleAssertions.cs" />
-    <Compile Include="..\System.CommandLine.Tests\Utility\OptionBuilder.cs" Link="Utility\OptionBuilder.cs" />
   </ItemGroup>
   
   <ItemGroup>

From 2717b4552586279a1145f9f681c5022208a21bbe Mon Sep 17 00:00:00 2001
From: Jon Sequeira <jonsequeira@gmail.com>
Date: Tue, 15 Mar 2022 10:55:53 -0700
Subject: [PATCH 06/11] wip

---
 ...indingCommandHandlerTests.BindingByName.cs |  2 +-
 .../ModelBindingCommandHandlerTests.cs        |  4 +-
 .../Binding/TypeConversionTests.cs            |  5 +-
 .../CompletionTests.cs                        | 34 ++++-----
 .../Help/HelpBuilderTests.Approval.cs         |  4 +-
 .../Help/HelpBuilderTests.cs                  |  6 +-
 src/System.CommandLine.Tests/OptionTests.cs   |  4 +-
 .../ParserTests.DoubleDash.cs                 |  2 +-
 src/System.CommandLine.Tests/ParserTests.cs   | 75 +++++++++----------
 .../ParsingValidationTests.cs                 | 11 ++-
 .../ResponseFileTests.cs                      | 20 ++---
 .../SuggestDirectiveTests.cs                  |  4 +-
 .../System.CommandLine.Tests.csproj           |  1 +
 src/System.CommandLine.Tests/UseHelpTests.cs  |  2 +-
 .../VersionOptionTests.cs                     |  2 +-
 src/System.CommandLine/Help/VersionOption.cs  |  4 +-
 src/System.CommandLine/Option.cs              |  4 +-
 17 files changed, 91 insertions(+), 93 deletions(-)

diff --git a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.BindingByName.cs b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.BindingByName.cs
index 156cd99b4a..2e7d9030d1 100644
--- a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.BindingByName.cs
+++ b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.BindingByName.cs
@@ -67,7 +67,7 @@ public async Task Option_arguments_are_bound_by_name_to_the_properties_of_method
 
             var command = new Command("the-command")
             {
-                new Option("--value", argumentType: type)
+                OptionBuilder.CreateOption("--value", type)
             };
 
             var console = new TestConsole();
diff --git a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs
index 97d12d9838..b145b45257 100644
--- a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs
+++ b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs
@@ -35,7 +35,7 @@ public async Task Unspecified_option_arguments_with_no_default_value_are_bound_t
 
         var command = new Command("command")
         {
-            new Option("-x", argumentType: parameterType)
+            OptionBuilder.CreateOption("-x", parameterType)
         };
 
         command.Handler = handler;
@@ -114,7 +114,7 @@ public async Task Handler_method_receives_option_arguments_bound_to_the_specifie
 
         var command = new Command("command")
         {
-            new Option("--value", argumentType: testCase.ParameterType)
+            OptionBuilder.CreateOption("--value", testCase.ParameterType)
         };
         command.Handler = handler;
 
diff --git a/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs b/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
index 434a2b2a41..40c6dc49e5 100644
--- a/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
+++ b/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
@@ -3,6 +3,7 @@
 
 using System.Collections;
 using System.Collections.Generic;
+using System.CommandLine.Utility;
 using System.IO;
 using FluentAssertions;
 using System.Linq;
@@ -748,8 +749,8 @@ public void Max_arity_greater_than_1_converts_to_enumerable_types(
             int maxArity,
             Type argumentType)
         {
-            var arity = new ArgumentArity(minArity, maxArity);
-            var option = new Option("--items", argumentType: argumentType, arity: arity);
+            var option = OptionBuilder.CreateOption("--items", valueType: argumentType);
+            option.Arity = new ArgumentArity(minArity, maxArity);
 
             var command = new RootCommand
             {
diff --git a/src/System.CommandLine.Tests/CompletionTests.cs b/src/System.CommandLine.Tests/CompletionTests.cs
index ddd85995e5..3fdbac7158 100644
--- a/src/System.CommandLine.Tests/CompletionTests.cs
+++ b/src/System.CommandLine.Tests/CompletionTests.cs
@@ -102,7 +102,7 @@ public void Command_GetCompletions_returns_available_subcommands_and_option_alia
             var command = new Command("command")
             {
                 new Command("subcommand"),
-                new Option("--option")
+                new Option<string>("--option")
             };
 
             var completions = command.GetCompletions();
@@ -239,9 +239,9 @@ public void When_one_option_has_been_specified_then_it_and_its_siblings_will_sti
         {
             var parser = new Command("command")
                          {
-                             new Option("--apple"),
-                             new Option("--banana"),
-                             new Option("--cherry")
+                             new Option<string>("--apple"),
+                             new Option<string>("--banana"),
+                             new Option<string>("--cherry")
                          };
 
             var commandLine = "--apple grannysmith";
@@ -261,15 +261,15 @@ public void When_a_subcommand_has_been_specified_then_its_sibling_commands_will_
             {
                 new Command("apple")
                 {
-                    new Option("--cortland")
+                    new Option<string>("--cortland")
                 },
                 new Command("banana")
                 {
-                    new Option("--cavendish")
+                    new Option<string>("--cavendish")
                 },
                 new Command("cherry")
                 {
-                    new Option("--rainier")
+                    new Option<string>("--rainier")
                 }
             };
 
@@ -285,13 +285,13 @@ public void When_a_subcommand_has_been_specified_then_its_sibling_commands_alias
         {
             var apple = new Command("apple")
             {
-                new Option("--cortland")
+                new Option<string>("--cortland")
             };
             apple.AddAlias("apl");
 
             var banana = new Command("banana")
             {
-                new Option("--cavendish")
+                new Option<string>("--cavendish")
             };
             banana.AddAlias("bnn");
 
@@ -315,7 +315,7 @@ public void When_a_subcommand_has_been_specified_then_its_sibling_options_will_n
             var command = new RootCommand("parent")
             {
                 new Command("child"), 
-                new Option("--parent-option")
+                new Option<string>("--parent-option")
             };
 
             var commandLine = "child";
@@ -402,9 +402,9 @@ public void When_one_option_has_been_partially_specified_then_nonmatching_siblin
         {
             var command = new Command("the-command")
             {
-                new Option("--apple"),
-                new Option("--banana"),
-                new Option("--cherry")
+                new Option<string>("--apple"),
+                new Option<string>("--banana"),
+                new Option<string>("--cherry")
             };
 
             var input = "a";
@@ -487,7 +487,7 @@ public void Both_subcommands_and_options_are_available_as_suggestions()
             var command = new Command("test")
             {
                 new Command("one"),
-                new Option("--one"),
+                new Option<string>("--one"),
                 new Argument
                 {
                     Arity = ArgumentArity.ExactlyOne
@@ -510,9 +510,9 @@ public void Option_GetCompletions_are_not_provided_without_matching_prefix(strin
         {
             var command = new Command("outer")
             {
-                new Option("--one"),
-                new Option("--two"),
-                new Option("--three")
+                new Option<string>("--one"),
+                new Option<string>("--two"),
+                new Option<string>("--three")
             };
 
             var parser = new Parser(command);
diff --git a/src/System.CommandLine.Tests/Help/HelpBuilderTests.Approval.cs b/src/System.CommandLine.Tests/Help/HelpBuilderTests.Approval.cs
index 09471953bb..77949afe8c 100644
--- a/src/System.CommandLine.Tests/Help/HelpBuilderTests.Approval.cs
+++ b/src/System.CommandLine.Tests/Help/HelpBuilderTests.Approval.cs
@@ -32,7 +32,7 @@ public void Help_layout_has_not_changed()
                 {
                     Description = "the-root-arg-enum-default-description"
                 },
-                new Option(aliases: new string[] {"--the-root-option-no-arg", "-trna"}) {
+                new Option<bool>(aliases: new string[] {"--the-root-option-no-arg", "-trna"}) {
                     Description = "the-root-option-no-arg-description",
                     IsRequired = true
                 },
@@ -60,7 +60,7 @@ public void Help_layout_has_not_changed()
                     Description = "the-root-option-description",
                     IsRequired = true
                 },
-                new Option(aliases: new string[] {"--the-root-option-multi-line-description", "-tromld"}) {
+                new Option<bool>(aliases: new string[] {"--the-root-option-multi-line-description", "-tromld"}) {
                     Description = "the-root-option\r\nmulti-line\ndescription"
                 }
             };
diff --git a/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs b/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
index 9853a1096d..38506a94d8 100644
--- a/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
+++ b/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
@@ -135,7 +135,7 @@ public void Usage_section_shows_arguments_if_there_are_arguments_for_command_whe
             var command = new Command("the-command", "command help")
             {
                 argument,
-                new Option(new[]
+                new Option<string>(new[]
                 {
                     "-v",
                     "--verbosity"
@@ -1235,7 +1235,7 @@ public void Options_aliases_differing_only_by_prefix_are_deduplicated_favoring_d
         {
             var command = new RootCommand
             {
-                new Option(new[] { "--long", "/long" })
+                new Option<string>(new[] { "--long", "/long" })
             };
 
             _helpBuilder.Write(command, _console);
@@ -1424,7 +1424,7 @@ public void Subcommands_properly_wraps_description()
                     {
                         Name = "inner-args"
                     },
-                    new Option(new[]
+                    new Option<string>(new[]
                     {
                         "-v",
                         "--verbosity"
diff --git a/src/System.CommandLine.Tests/OptionTests.cs b/src/System.CommandLine.Tests/OptionTests.cs
index 7d87ebc5f3..012d83406a 100644
--- a/src/System.CommandLine.Tests/OptionTests.cs
+++ b/src/System.CommandLine.Tests/OptionTests.cs
@@ -172,7 +172,7 @@ public void Raw_aliases_are_exposed_by_an_option()
         public void When_an_option_is_created_with_an_alias_that_contains_whitespace_then_an_informative_error_is_returned(
             string alias)
         {
-            Action create = () => new Option(alias);
+            Action create = () => new Option<string>(alias);
 
             create.Should()
                   .Throw<ArgumentException>()
@@ -372,6 +372,6 @@ public void Option_of_boolean_defaults_to_false_when_not_specified()
                 .BeFalse();
         }
         
-        protected override Symbol CreateSymbol(string name) => new Option(name);
+        protected override Symbol CreateSymbol(string name) => new Option<string>(name);
     }
 }
diff --git a/src/System.CommandLine.Tests/ParserTests.DoubleDash.cs b/src/System.CommandLine.Tests/ParserTests.DoubleDash.cs
index 210105db59..91deff417c 100644
--- a/src/System.CommandLine.Tests/ParserTests.DoubleDash.cs
+++ b/src/System.CommandLine.Tests/ParserTests.DoubleDash.cs
@@ -101,7 +101,7 @@ public class LegacyDoubleDashBehavior
             [Fact]
             public void The_portion_of_the_command_line_following_a_double_is_treated_as_unparsed_tokens()
             {
-                var result = new CommandLineBuilder(new RootCommand { new Option("-o") })
+                var result = new CommandLineBuilder(new RootCommand { new Option<string>("-o") })
                              .EnableLegacyDoubleDashBehavior()
                              .Build()
                              .Parse("-o \"some stuff\" -- x y z");
diff --git a/src/System.CommandLine.Tests/ParserTests.cs b/src/System.CommandLine.Tests/ParserTests.cs
index 0c68f14d23..8f2e184c39 100644
--- a/src/System.CommandLine.Tests/ParserTests.cs
+++ b/src/System.CommandLine.Tests/ParserTests.cs
@@ -73,7 +73,7 @@ public void When_a_token_is_just_a_prefix_then_an_error_is_returned(string prefi
         [Fact]
         public void Short_form_options_can_be_specified_using_equals_delimiter()
         {
-            var option = new Option<string>("-x") { Arity = ArgumentArity.ExactlyOne };
+            var option = new Option<string>("-x");
 
             var result = option.Parse("-x=some-value");
 
@@ -85,8 +85,7 @@ public void Short_form_options_can_be_specified_using_equals_delimiter()
         [Fact]
         public void Long_form_options_can_be_specified_using_equals_delimiter()
         {
-            var option = 
-                new Option("--hello") { Arity = ArgumentArity.ExactlyOne };
+            var option = new Option<string>("--hello");
 
             var result = option.Parse("--hello=there");
 
@@ -110,7 +109,7 @@ public void Short_form_options_can_be_specified_using_colon_delimiter()
         [Fact]
         public void Long_form_options_can_be_specified_using_colon_delimiter()
         {
-            var option = new Option("--hello") { Arity = ArgumentArity.ExactlyOne };
+            var option = new Option<string>("--hello");
 
             var result = option.Parse("--hello:there");
 
@@ -231,7 +230,7 @@ public void Required_option_arguments_are_not_unbundled()
         [Fact]
         public void Last_bundled_option_can_accept_argument_with_no_separator()
         {
-            var optionA = new Option("-a");
+            var optionA = new Option<bool>("-a");
             var optionB = new Option<string>("-b") { Arity = ArgumentArity.ZeroOrOne };
             var optionC = new Option<string>("-c") { Arity = ArgumentArity.ExactlyOne };
 
@@ -255,7 +254,7 @@ public void Last_bundled_option_can_accept_argument_with_no_separator()
         [Fact]
         public void Last_bundled_option_can_accept_argument_with_equals_separator()
         {
-            var optionA = new Option("-a");
+            var optionA = new Option<bool>("-a");
             var optionB = new Option<string>("-b") { Arity = ArgumentArity.ZeroOrOne };
             var optionC = new Option<string>("-c") { Arity = ArgumentArity.ExactlyOne };
 
@@ -279,7 +278,7 @@ public void Last_bundled_option_can_accept_argument_with_equals_separator()
         [Fact]
         public void Last_bundled_option_can_accept_argument_with_colon_separator()
         {
-            var optionA = new Option("-a");
+            var optionA = new Option<bool>("-a");
             var optionB = new Option<string>("-b") { Arity = ArgumentArity.ZeroOrOne };
             var optionC = new Option<string>("-c") { Arity = ArgumentArity.ExactlyOne };
 
@@ -303,7 +302,7 @@ public void Last_bundled_option_can_accept_argument_with_colon_separator()
         [Fact]
         public void Invalid_char_in_bundle_causes_rest_to_be_interpreted_as_value()
         {
-            var optionA = new Option("-a");
+            var optionA = new Option<bool>("-a");
             var optionB = new Option<string>("-b") { Arity = ArgumentArity.ZeroOrOne };
             var optionC = new Option<string>("-c") { Arity = ArgumentArity.ExactlyOne };
 
@@ -422,8 +421,8 @@ public void Command_with_multiple_options_is_parsed_correctly()
         {
             var option = new Command("outer")
             {
-                new Option("--inner1") { Arity = ArgumentArity.ExactlyOne },
-                new Option("--inner2") { Arity = ArgumentArity.ExactlyOne }
+                new Option<string>("--inner1"),
+                new Option<string>("--inner2")
             };
 
             var parser = new Parser(option);
@@ -598,7 +597,7 @@ public void Nested_commands_with_colliding_names_cannot_both_be_applied()
         [Fact]
         public void When_child_option_will_not_accept_arg_then_parent_can()
         {
-            var option = new Option("-x");
+            var option = new Option<bool>("-x");
             var command = new Command("the-command")
                          {
                              option,
@@ -607,7 +606,8 @@ public void When_child_option_will_not_accept_arg_then_parent_can()
 
             var result = command.Parse("the-command -x the-argument");
 
-            result.FindResultFor(option).Tokens.Should().BeEmpty();
+            var optionResult = result.FindResultFor(option);
+            optionResult.Tokens.Should().BeEmpty();
             result.CommandResult.Tokens.Select(t => t.Value).Should().BeEquivalentTo("the-argument");
         }
 
@@ -670,9 +670,9 @@ public void When_options_with_the_same_name_are_defined_on_parent_and_child_comm
                         {
                             new Command("inner")
                             {
-                                new Option("-x")
+                                new Option<bool>("-x")
                             },
-                            new Option("-x")
+                            new Option<bool>("-x")
                         };
 
             ParseResult result = outer.Parse("outer inner -x");
@@ -692,9 +692,9 @@ public void When_options_with_the_same_name_are_defined_on_parent_and_child_comm
         public void When_options_with_the_same_name_are_defined_on_parent_and_child_commands_and_specified_in_between_then_it_attaches_to_the_outer_command()
         {
             var outer = new Command("outer");
-            outer.AddOption(new Option("-x"));
+            outer.AddOption(new Option<bool>("-x"));
             var inner = new Command("inner");
-            inner.AddOption(new Option("-x"));
+            inner.AddOption(new Option<bool>("-x"));
             outer.AddCommand(inner);
 
             var result = outer.Parse("outer -x inner");
@@ -994,14 +994,13 @@ public void Command_default_argument_value_does_not_override_parsed_value()
         }
 
         [Fact]
-        public void Unmatched_options_are_not_split_into_smaller_tokens()
+        public void Unmatched_tokens_that_look_like_options_are_not_split_into_smaller_tokens()
         {
             var outer = new Command("outer")
             {
-                new Option("-p"),
                 new Command("inner")
                 {
-                    new Argument
+                    new Argument<string[]>
                     {
                         Arity = ArgumentArity.OneOrMore
                     }
@@ -1043,22 +1042,16 @@ public void Option_and_Command_can_have_the_same_alias()
         {
             var innerCommand = new Command("inner")
             {
-                new Argument
-                {
-                    Arity = ArgumentArity.ZeroOrMore
-                }
+                new Argument<string[]>()
             };
 
-            var option = new Option("--inner");
+            var option = new Option<bool>("--inner");
 
             var outerCommand = new Command("outer")
             {
                 innerCommand,
                 option,
-                new Argument
-                {
-                    Arity = ArgumentArity.ZeroOrMore
-                }
+                new Argument<string[]>()
             };
 
             var parser = new Parser(outerCommand);
@@ -1092,8 +1085,8 @@ public void Option_and_Command_can_have_the_same_alias()
         [Fact]
         public void Options_can_have_the_same_alias_differentiated_only_by_prefix()
         {
-            var option1 = new Option(new[] { "-a" });
-            var option2 = new Option(new[] { "--a" });
+            var option1 = new Option<bool>(new[] { "-a" });
+            var option2 = new Option<bool>(new[] { "--a" });
 
             var parser = new RootCommand
             {
@@ -1124,7 +1117,7 @@ public void When_an_option_argument_is_enclosed_in_double_quotes_its_value_retai
             string arg1,
             string arg2)
         {
-            var option = new Option("-x") { Arity = ArgumentArity.ZeroOrMore };
+            var option = new Option<string[]>("-x");
 
             var parseResult = option.Parse(new[] { arg1, arg2 });
 
@@ -1165,12 +1158,12 @@ public void Trailing_option_delimiters_are_ignored()
         [InlineData("-x:-y")]
         public void Option_arguments_can_start_with_prefixes_that_make_them_look_like_options(string input)
         {
-            var optionX = new Option("-x") { Arity = ArgumentArity.ZeroOrOne};
+            var optionX = new Option<string>("-x");
 
             var command = new Command("command")
             {
                 optionX,
-                new Option("-z") { Arity = ArgumentArity.ZeroOrOne}
+                new Option<string>("-z")
             };
 
             var result = command.Parse(input);
@@ -1246,12 +1239,12 @@ public void Arguments_can_match_subcommands()
         [InlineData("-x:-y")]
         public void Option_arguments_can_match_the_aliases_of_sibling_options_when_non_space_argument_delimiter_is_used(string input)
         {
-            var optionX = new Option("-x") { Arity = ArgumentArity.ZeroOrOne };
+            var optionX = new Option<string>("-x");
 
             var command = new Command("command")
             {
                 optionX,
-                new Option("-y") { Arity = ArgumentArity.ZeroOrOne }
+                new Option<string>("-y")
             };
 
             var result = command.Parse(input);
@@ -1363,7 +1356,7 @@ public void Argument_name_is_not_matched_as_a_token()
         [Fact]
         public void Option_aliases_do_not_need_to_be_prefixed()
         {
-            var option = new Option("noprefix");
+            var option = new Option<bool>("noprefix");
 
             var result = new RootCommand { option }.Parse("noprefix");
 
@@ -1394,7 +1387,7 @@ public void When_a_command_line_has_unmatched_tokens_they_are_not_applied_to_sub
             };
             var optionX = new Option<string>("-x");
             command.AddOption(optionX);
-            var optionY = new Option("-y") { Arity = ArgumentArity.ExactlyOne };
+            var optionY = new Option<string>("-y");
             command.AddOption(optionY);
 
             var result = command.Parse("-x 23 unmatched-token -y 42");
@@ -1510,7 +1503,7 @@ public void When_command_arguments_are_greater_than_maximum_arity_then_an_error_
         [Fact]
         public void Option_argument_arity_can_be_a_fixed_value_greater_than_1()
         {
-            var option = new Option("-x") { Arity = new ArgumentArity(3, 3)};
+            var option = new Option<int[]>("-x") { Arity = new ArgumentArity(3, 3)};
 
             var command = new Command("the-command")
             {
@@ -1530,7 +1523,7 @@ public void Option_argument_arity_can_be_a_fixed_value_greater_than_1()
         [Fact]
         public void Option_argument_arity_can_be_a_range_with_a_lower_bound_greater_than_1()
         {
-            var option = new Option("-x") { Arity = new ArgumentArity(3, 5) };
+            var option = new Option<string[]>("-x") { Arity = new ArgumentArity(3, 5) };
 
             var command = new Command("the-command")
             {
@@ -1560,7 +1553,7 @@ public void Option_argument_arity_can_be_a_range_with_a_lower_bound_greater_than
         [Fact]
         public void When_option_arguments_are_fewer_than_minimum_arity_then_an_error_is_returned()
         {
-            var option = new Option("-x") { Arity = new ArgumentArity(2, 3) };
+            var option = new Option<int[]>("-x") { Arity = new ArgumentArity(2, 3) };
 
             var command = new Command("the-command")
             {
@@ -1580,7 +1573,7 @@ public void When_option_arguments_are_greater_than_maximum_arity_then_an_error_i
         {
             var command = new Command("the-command")
             {
-                new Option("-x") { Arity = new ArgumentArity(2, 3)}
+                new Option<int[]>("-x") { Arity = new ArgumentArity(2, 3)}
             };
 
             command.Parse("-x 1 2 3 4")
diff --git a/src/System.CommandLine.Tests/ParsingValidationTests.cs b/src/System.CommandLine.Tests/ParsingValidationTests.cs
index 555ce97caf..d4645a62a4 100644
--- a/src/System.CommandLine.Tests/ParsingValidationTests.cs
+++ b/src/System.CommandLine.Tests/ParsingValidationTests.cs
@@ -158,7 +158,7 @@ public void When_a_required_option_is_not_supplied_then_an_error_is_returned()
         {
             var command = new Command("command")
             {
-                new Option("-x")
+                new Option<string>("-x")
                 {
                     IsRequired = true
                 }
@@ -224,7 +224,10 @@ public void When_no_option_accepts_arguments_but_one_is_supplied_then_an_error_i
             var parser = new Parser(
                 new Command("the-command")
                 {
-                    new Option("-x")
+                    new Option<bool>("-x")
+                    {
+                        Arity = ArgumentArity.Zero
+                    }
                 });
 
             var result = parser.Parse("the-command -x some-arg");
@@ -244,8 +247,8 @@ public void A_custom_validator_can_be_added_to_a_command()
         {
             var command = new Command("the-command")
             {
-                new Option("--one"),
-                new Option("--two")
+                new Option<bool>("--one"),
+                new Option<bool>("--two")
             };
 
             command.AddValidator(commandResult =>
diff --git a/src/System.CommandLine.Tests/ResponseFileTests.cs b/src/System.CommandLine.Tests/ResponseFileTests.cs
index 8acbba2ea8..2bf64ad29f 100644
--- a/src/System.CommandLine.Tests/ResponseFileTests.cs
+++ b/src/System.CommandLine.Tests/ResponseFileTests.cs
@@ -44,7 +44,7 @@ private string ResponseFile(params string[] lines)
         [Fact]
         public void When_response_file_specified_it_loads_options_from_response_file()
         {
-            var option = new Option("--flag");
+            var option = new Option<bool>("--flag");
 
             var result = option.Parse($"@{ResponseFile("--flag")}");
 
@@ -59,7 +59,7 @@ public void When_response_file_is_specified_it_loads_options_with_arguments_from
                 "--flag2",
                 "123");
 
-            var optionOne = new Option("--flag");
+            var optionOne = new Option<bool>("--flag");
 
             var optionTwo = new Option<int>("--flag2");
             var result = new RootCommand
@@ -187,8 +187,8 @@ public void Response_file_can_contain_blank_lines()
         [Fact]
         public void Response_file_can_contain_comments_which_are_ignored_when_loaded()
         {
-            var optionOne = new Option("--flag");
-            var optionTwo = new Option("--flag2");
+            var optionOne = new Option<bool>("--flag");
+            var optionTwo = new Option<bool>("--flag2");
 
             var responseFile = ResponseFile(
                 "# comment one",
@@ -212,8 +212,8 @@ public void Response_file_can_contain_comments_which_are_ignored_when_loaded()
         [Fact]
         public void When_response_file_does_not_exist_then_error_is_returned()
         {
-            var optionOne = new Option("--flag");
-            var optionTwo = new Option("--flag2");
+            var optionOne = new Option<bool>("--flag");
+            var optionTwo = new Option<bool>("--flag2");
 
             var result = new RootCommand
                          {
@@ -230,8 +230,8 @@ public void When_response_file_does_not_exist_then_error_is_returned()
         [Fact]
         public void When_response_filepath_is_not_specified_then_error_is_returned()
         {
-            var optionOne = new Option("--flag");
-            var optionTwo = new Option("--flag2");
+            var optionOne = new Option<bool>("--flag");
+            var optionTwo = new Option<bool>("--flag2");
 
             var result = new RootCommand
                          {
@@ -254,8 +254,8 @@ public void When_response_filepath_is_not_specified_then_error_is_returned()
         public void When_response_file_cannot_be_read_then_specified_error_is_returned()
         {
             var nonexistent = Path.GetTempFileName();
-            var optionOne = new Option("--flag");
-            var optionTwo = new Option("--flag2");
+            var optionOne = new Option<bool>("--flag");
+            var optionTwo = new Option<bool>("--flag2");
 
             using (File.Open(nonexistent, FileMode.Open, FileAccess.ReadWrite, FileShare.None))
             {
diff --git a/src/System.CommandLine.Tests/SuggestDirectiveTests.cs b/src/System.CommandLine.Tests/SuggestDirectiveTests.cs
index 38b3f85f4a..4849ce2cb3 100644
--- a/src/System.CommandLine.Tests/SuggestDirectiveTests.cs
+++ b/src/System.CommandLine.Tests/SuggestDirectiveTests.cs
@@ -228,8 +228,8 @@ public async Task It_writes_suggestions_for_partial_option_and_subcommand_aliase
             var parser = new CommandLineBuilder(new Command("parent")
                           {
                               new Command("child"),
-                              new Option("--option1"),
-                              new Option("--option2"),
+                              new Option<bool>("--option1"),
+                              new Option<bool>("--option2"),
                               new Argument<string>()
                           })
                           .UseSuggestDirective()
diff --git a/src/System.CommandLine.Tests/System.CommandLine.Tests.csproj b/src/System.CommandLine.Tests/System.CommandLine.Tests.csproj
index 486e4e1d54..955d965fb1 100644
--- a/src/System.CommandLine.Tests/System.CommandLine.Tests.csproj
+++ b/src/System.CommandLine.Tests/System.CommandLine.Tests.csproj
@@ -29,6 +29,7 @@
   </ItemGroup>
   
   <ItemGroup>
+    <Compile Include="..\Common\OptionBuilder.cs" Link="Utility\OptionBuilder.cs" />
     <Compile Include="..\System.CommandLine.Suggest\DotnetMuxer.cs" Link="Utility\DotnetMuxer.cs" />
   </ItemGroup>
   
diff --git a/src/System.CommandLine.Tests/UseHelpTests.cs b/src/System.CommandLine.Tests/UseHelpTests.cs
index 2d9ec07f48..489228f411 100644
--- a/src/System.CommandLine.Tests/UseHelpTests.cs
+++ b/src/System.CommandLine.Tests/UseHelpTests.cs
@@ -87,7 +87,7 @@ public async Task UseHelp_accepts_default_values(string value)
         public async Task UseHelp_does_not_display_when_option_defined_with_same_alias()
         {
             var command = new Command("command");
-            command.AddOption(new Option("-h"));
+            command.AddOption(new Option<bool>("-h"));
             
             var parser =
                 new CommandLineBuilder(new RootCommand
diff --git a/src/System.CommandLine.Tests/VersionOptionTests.cs b/src/System.CommandLine.Tests/VersionOptionTests.cs
index 046b863876..4671567a3b 100644
--- a/src/System.CommandLine.Tests/VersionOptionTests.cs
+++ b/src/System.CommandLine.Tests/VersionOptionTests.cs
@@ -120,7 +120,7 @@ public void Version_is_not_valid_with_other_tokens(string commandLine)
             var rootCommand = new RootCommand
             {
                 subcommand,
-                new Option("-x")
+                new Option<bool>("-x")
             };
             rootCommand.SetHandler(() => { });
 
diff --git a/src/System.CommandLine/Help/VersionOption.cs b/src/System.CommandLine/Help/VersionOption.cs
index 4a7766a431..602478797e 100644
--- a/src/System.CommandLine/Help/VersionOption.cs
+++ b/src/System.CommandLine/Help/VersionOption.cs
@@ -7,7 +7,7 @@
 
 namespace System.CommandLine.Help
 {
-    internal class VersionOption : Option
+    internal class VersionOption : Option<bool>
     {
         private readonly CommandLineBuilder _builder;
         private string? _description;
@@ -15,7 +15,7 @@ internal class VersionOption : Option
         public VersionOption(CommandLineBuilder builder) : base("--version")
         {
             _builder = builder;
-
+            
             DisallowBinding = true;
 
             AddValidators();
diff --git a/src/System.CommandLine/Option.cs b/src/System.CommandLine/Option.cs
index 27a3d2cff3..5223f5b747 100644
--- a/src/System.CommandLine/Option.cs
+++ b/src/System.CommandLine/Option.cs
@@ -21,10 +21,10 @@ public class Option : IdentifierSymbol, IValueDescriptor
 
         // FIX: (Option) delete temp constructors
 
-        public Option(string name) : this(name, description: null)
+        public Option(string[] aliases) : this(aliases, description: null)
         {
         }
-
+        
         /// <summary>
         /// Initializes a new instance of the <see cref="Option"/> class.
         /// </summary>

From 703cef9068b0240d0b39b7ae0b7b27db49ec9b6e Mon Sep 17 00:00:00 2001
From: Jon Sequeira <jonsequeira@gmail.com>
Date: Tue, 15 Mar 2022 12:11:26 -0700
Subject: [PATCH 07/11] make Option (non-generic) abstract

---
 .../Help/HelpBuilderTests.cs                  | 35 +++++++--------
 .../OptionTests.MultipleArgumentsPerToken.cs  | 12 +++--
 src/System.CommandLine.Tests/OptionTests.cs   |  3 +-
 .../ParseResultTests.cs                       |  2 +-
 .../ParserTests.DoubleDash.cs                 |  8 ++--
 src/System.CommandLine.Tests/ParserTests.cs   | 12 ++---
 src/System.CommandLine/Help/HelpOption.cs     |  2 +-
 src/System.CommandLine/Option.cs              | 45 +------------------
 8 files changed, 37 insertions(+), 82 deletions(-)

diff --git a/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs b/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
index 38506a94d8..573336a6e2 100644
--- a/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
+++ b/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
@@ -185,7 +185,7 @@ public void Usage_section_shows_arguments_if_there_are_arguments_for_command_whe
             {
                 arg1,
                 arg2,
-                new Option(new[] { "-v", "--verbosity" }, "Sets the verbosity")
+                new Option<string>(new[] { "-v", "--verbosity" }, "Sets the verbosity")
             };
 
             var rootCommand = new RootCommand();
@@ -435,8 +435,7 @@ public void Arguments_section_is_not_included_if_there_are_options_with_no_argum
         {
             var command = new RootCommand
             {
-                new Option(new[] { "-v", "--verbosity" },
-                           "Sets the verbosity.")
+                new Option<string>(new[] { "-v", "--verbosity" }, "Sets the verbosity.")
             };
 
             _helpBuilder.Write(command, _console);
@@ -465,7 +464,7 @@ public void Arguments_section_includes_configured_argument_aliases()
         {
             var command = new Command("the-command", "command help")
             {
-                new Option(new[] { "-v", "--verbosity" }, arity: ArgumentArity.ExactlyOne)
+                new Option<string>(new[] { "-v", "--verbosity" })
                 {
                     ArgumentHelpName = "LEVEL",
                     Description = "Sets the verbosity."
@@ -1013,9 +1012,9 @@ public void Options_section_aligns_options_on_new_lines()
                               "the-command",
                               "Help text for the command")
                           {
-                              new Option(new[] { "-a", "--aaa" },
+                              new Option<string>(new[] { "-a", "--aaa" },
                                          "An option with 8 characters"),
-                              new Option(new[] { "-b", "--bbbbbbbbbb" },
+                              new Option<string>(new[] { "-b", "--bbbbbbbbbb" },
                                          "An option with 15 characters")
                           };
 
@@ -1037,7 +1036,7 @@ public void Retains_single_dash_on_multi_char_option()
         {
             var command = new Command("command", "Help Test")
                           {
-                              new Option(
+                              new Option<string>(
                                   new[] { "-multi", "--alt-option" },
                                   "HelpDetail for option")
                           };
@@ -1054,7 +1053,7 @@ public void Options_section_retains_multiple_dashes_on_single_char_option()
         {
             var command = new Command("command", "Help Test")
                           {
-                              new Option(
+                              new Option<string>(
                                   new[] { "--m", "--alt-option" },
                                   "HelpDetail for option")
                           };
@@ -1072,7 +1071,7 @@ public void Options_section_keeps_added_newlines()
                     "test-command",
                     "Help text for the command")
                 {
-                    new Option(
+                    new Option<bool>(
                         new[] { "-a", "--aaa" },
                         $"Help{NewLine}for \r\n the\noption")
                 };
@@ -1098,7 +1097,7 @@ public void Options_section_properly_wraps_description()
             var command = new Command("test-command", "Help text for the command")
             {
                 new Option<string>("-x", "Option with a short description"),
-                new Option(new[] { "-a", "--aaa" }, longOptionText),
+                new Option<bool>(new[] { "-a", "--aaa" }, longOptionText),
                 new Option<string>("-y", "Option with a short description"),
             };
 
@@ -1123,7 +1122,7 @@ public void Options_section_properly_wraps_description_when_long_default_value_i
             var command = new Command("test-command", "Help text for the command")
             {
                 new Option<string>("-x", "Option with a short description"),
-                new Option(new[] { "-a", "--aaa" }, longOptionText, getDefaultValue: () => "the quick brown fox jumps over the lazy dog"),
+                new Option<string>(new[] { "-a", "--aaa" }, description: longOptionText, getDefaultValue: () => "the quick brown fox jumps over the lazy dog"),
                 new Option<string>("-y", "Option with a short description"),
             };
 
@@ -1220,7 +1219,7 @@ public void Options_aliases_differing_only_by_prefix_are_deduplicated_favoring_d
         {
             var command = new RootCommand
             {
-                new Option(new[] { "-x", "/x" })
+                new Option<string>(new[] { "-x", "/x" })
             };
 
             _helpBuilder.Write(command, _console);
@@ -1250,10 +1249,10 @@ public void Options_help_preserves_the_order_options_are_added_the_the_parent_co
         {
             var command = new RootCommand
             {
-                new Option(new[] { "--first", "-f" }),
-                new Option(new[] { "--second", "-s" }),
-                new Option(new[] { "--third" }),
-                new Option(new[] { "--last", "-l" })
+                new Option<bool>(new[] { "--first", "-f" }),
+                new Option<bool>(new[] { "--second", "-s" }),
+                new Option<bool>(new[] { "--third" }),
+                new Option<bool>(new[] { "--last", "-l" })
             };
 
             _helpBuilder.Write(command, _console);
@@ -1274,7 +1273,7 @@ public void Option_aliases_are_shown_before_long_names_regardless_of_alphabetica
         {
             var command = new RootCommand
             {
-                new Option(new[] { "-z", "-a", "--zzz", "--aaa" })
+                new Option<string>(new[] { "-z", "-a", "--zzz", "--aaa" })
             };
 
             _helpBuilder.Write(command, _console);
@@ -1287,7 +1286,7 @@ public void Help_describes_default_value_for_option_with_argument_having_default
         {
             var command = new Command("the-command", "command help")
             {
-                new Option(new[] { "-arg"}, getDefaultValue: () => "the-arg-value")
+                new Option<string>(new[] { "-arg"}, getDefaultValue: () => "the-arg-value")
                 {
                     ArgumentHelpName = "the-arg"
                 }
diff --git a/src/System.CommandLine.Tests/OptionTests.MultipleArgumentsPerToken.cs b/src/System.CommandLine.Tests/OptionTests.MultipleArgumentsPerToken.cs
index c3ded7f611..1eb8242b63 100644
--- a/src/System.CommandLine.Tests/OptionTests.MultipleArgumentsPerToken.cs
+++ b/src/System.CommandLine.Tests/OptionTests.MultipleArgumentsPerToken.cs
@@ -26,12 +26,11 @@ public Allowed(ITestOutputHelper output)
                 [Fact]
                 public void When_option_is_not_respecified_but_limit_is_not_reached_then_the_following_token_is_used_as_value()
                 {
-                    var animalsOption = new Option(new[] { "-a", "--animals" })
+                    var animalsOption = new Option<string[]>(new[] { "-a", "--animals" })
                     {
                         AllowMultipleArgumentsPerToken = true,
-                        Arity = ArgumentArity.ZeroOrMore
                     };
-                    var vegetablesOption = new Option(new[] { "-v", "--vegetables" }) { Arity = ArgumentArity.ZeroOrMore };
+                    var vegetablesOption = new Option<string>(new[] { "-v", "--vegetables" });
 
                     var command = new RootCommand
                     {
@@ -64,12 +63,11 @@ public void When_option_is_not_respecified_but_limit_is_not_reached_then_the_fol
                 [Fact]
                 public void When_option_is_not_respecified_and_limit_is_reached_then_the_following_token_is_unmatched()
                 {
-                    var animalsOption = new Option(new[] { "-a", "--animals" })
+                    var animalsOption = new Option<string>(new[] { "-a", "--animals" })
                     {
-                        AllowMultipleArgumentsPerToken = true,
-                        Arity = ArgumentArity.ZeroOrOne
+                        AllowMultipleArgumentsPerToken = true
                     };
-                    var vegetablesOption = new Option(new[] { "-v", "--vegetables" }) { Arity = ArgumentArity.ZeroOrMore };
+                    var vegetablesOption = new Option<string[]>(new[] { "-v", "--vegetables" });
 
                     var command = new RootCommand
                     {
diff --git a/src/System.CommandLine.Tests/OptionTests.cs b/src/System.CommandLine.Tests/OptionTests.cs
index 012d83406a..f4a7f8a23f 100644
--- a/src/System.CommandLine.Tests/OptionTests.cs
+++ b/src/System.CommandLine.Tests/OptionTests.cs
@@ -1,7 +1,6 @@
 // Copyright (c) .NET Foundation and contributors. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
-using System.Collections.Generic;
 using System.CommandLine.Parsing;
 using System.Linq;
 using FluentAssertions;
@@ -14,7 +13,7 @@ public partial class OptionTests : SymbolTests
         [Fact]
         public void When_an_option_has_only_one_alias_then_that_alias_is_its_name()
         {
-            var option = new Option(new[] { "myname" });
+            var option = new Option<string>(new[] { "myname" });
 
             option.Name.Should().Be("myname");
         }
diff --git a/src/System.CommandLine.Tests/ParseResultTests.cs b/src/System.CommandLine.Tests/ParseResultTests.cs
index c7d37ec438..fef5f791a6 100644
--- a/src/System.CommandLine.Tests/ParseResultTests.cs
+++ b/src/System.CommandLine.Tests/ParseResultTests.cs
@@ -26,7 +26,7 @@ public void An_option_with_a_default_value_and_no_explicitly_provided_argument_h
         [Fact]
         public void HasOption_can_be_used_to_check_the_presence_of_an_option()
         {
-            var option = new Option(new[] { "-h", "--help" });
+            var option = new Option<bool>(new[] { "-h", "--help" });
 
             var command = new Command("the-command")
             {
diff --git a/src/System.CommandLine.Tests/ParserTests.DoubleDash.cs b/src/System.CommandLine.Tests/ParserTests.DoubleDash.cs
index 91deff417c..c4546dc25a 100644
--- a/src/System.CommandLine.Tests/ParserTests.DoubleDash.cs
+++ b/src/System.CommandLine.Tests/ParserTests.DoubleDash.cs
@@ -114,10 +114,10 @@ public void The_portion_of_the_command_line_following_a_double_is_treated_as_unp
             [Fact]
             public void Subsequent_tokens_matching_options_will_be_treated_as_unparsed_tokens()
             {
-                var optionO = new Option(new[] { "-o" });
-                var optionX = new Option(new[] { "-x" });
-                var optionY = new Option(new[] { "-y" });
-                var optionZ = new Option(new[] { "-z" });
+                var optionO = new Option<string>(new[] { "-o" });
+                var optionX = new Option<bool>(new[] { "-x" });
+                var optionY = new Option<bool>(new[] { "-y" });
+                var optionZ = new Option<bool>(new[] { "-z" });
                 var rootCommand = new RootCommand
                 {
                     optionO,
diff --git a/src/System.CommandLine.Tests/ParserTests.cs b/src/System.CommandLine.Tests/ParserTests.cs
index 8f2e184c39..ed0ba66bf6 100644
--- a/src/System.CommandLine.Tests/ParserTests.cs
+++ b/src/System.CommandLine.Tests/ParserTests.cs
@@ -328,8 +328,8 @@ public void Invalid_char_in_bundle_causes_rest_to_be_interpreted_as_value()
         [Fact]
         public void Parser_root_Options_can_be_specified_multiple_times_and_their_arguments_are_collated()
         {
-            var animalsOption = new Option(new[] { "-a", "--animals" }) { Arity = ArgumentArity.ZeroOrMore };
-            var vegetablesOption = new Option(new[] { "-v", "--vegetables" }) { Arity = ArgumentArity.ZeroOrMore };
+            var animalsOption = new Option<string[]>(new[] { "-a", "--animals" });
+            var vegetablesOption = new Option<string[]>(new[] { "-v", "--vegetables" });
             var parser = new RootCommand
             {
                 animalsOption,
@@ -354,9 +354,9 @@ public void Parser_root_Options_can_be_specified_multiple_times_and_their_argume
         [Fact]
         public void Options_can_be_specified_multiple_times_and_their_arguments_are_collated()
         {
-            var animalsOption = new Option(new[] { "-a", "--animals" }) { Arity = ArgumentArity.ZeroOrMore}
+            var animalsOption = new Option<string[]>(new[] { "-a", "--animals" })
                 .FromAmong("dog", "cat", "sheep");
-            var vegetablesOption = new Option(new[] { "-v", "--vegetables" }) { Arity = ArgumentArity.ZeroOrMore };
+            var vegetablesOption = new Option<string[]>(new[] { "-v", "--vegetables" });
             var parser = new Parser(
                 new Command("the-command") {
                     animalsOption,
@@ -381,9 +381,9 @@ public void Options_can_be_specified_multiple_times_and_their_arguments_are_coll
         [Fact]
         public void When_an_option_is_not_respecified_but_limit_is_reached_then_the_following_token_is_considered_an_argument_to_the_parent_command()
         {
-            var animalsOption = new Option(new[] { "-a", "--animals" }) { Arity = ArgumentArity.ZeroOrOne };
+            var animalsOption = new Option<string[]>(new[] { "-a", "--animals" });
 
-            var vegetablesOption = new Option(new[] { "-v", "--vegetables" }) { Arity = ArgumentArity.ZeroOrOne };
+            var vegetablesOption = new Option<string[]>(new[] { "-v", "--vegetables" });
             
             var parser = new Parser(
                 new Command("the-command")
diff --git a/src/System.CommandLine/Help/HelpOption.cs b/src/System.CommandLine/Help/HelpOption.cs
index 9033dc11af..5bf9b9c33c 100644
--- a/src/System.CommandLine/Help/HelpOption.cs
+++ b/src/System.CommandLine/Help/HelpOption.cs
@@ -3,7 +3,7 @@
 
 namespace System.CommandLine.Help
 {
-    internal class HelpOption : Option
+    internal class HelpOption : Option<bool>
     {
         private readonly Func<LocalizationResources> _localizationResources;
         private string? _description;
diff --git a/src/System.CommandLine/Option.cs b/src/System.CommandLine/Option.cs
index 5223f5b747..30dbf7c6cc 100644
--- a/src/System.CommandLine/Option.cs
+++ b/src/System.CommandLine/Option.cs
@@ -12,54 +12,13 @@ namespace System.CommandLine
     /// <summary>
     /// A symbol defining a named parameter and a value for that parameter. 
     /// </summary>
-    /// <seealso cref="System.CommandLine.IdentifierSymbol" />
-    public class Option : IdentifierSymbol, IValueDescriptor
+    /// <seealso cref="IdentifierSymbol" />
+    public abstract class Option : IdentifierSymbol, IValueDescriptor
     {
         private string? _name;
         private List<ValidateSymbolResult<OptionResult>>? _validators;
         private Argument? _argument;
 
-        // FIX: (Option) delete temp constructors
-
-        public Option(string[] aliases) : this(aliases, description: null)
-        {
-        }
-        
-        /// <summary>
-        /// Initializes a new instance of the <see cref="Option"/> class.
-        /// </summary>
-        /// <param name="name">The name of the option, which can be used to specify it on the command line.</param>
-        /// <param name="description">The description of the option shown in help.</param>
-        /// <param name="argumentType">The type that the option's argument(s) can be parsed to.</param>
-        /// <param name="getDefaultValue">A delegate used to get a default value for the option when it is not specified on the command line.</param>
-        /// <param name="arity">The arity of the option.</param>
-        public Option(
-            string name,
-            string? description = null,
-            Type? argumentType = null,
-            Func<object?>? getDefaultValue = null,
-            ArgumentArity arity = default)
-            : this(name, description, CreateArgument(argumentType, getDefaultValue, arity))
-        {
-        }
-
-        /// <summary>
-        /// Initializes a new instance of the <see cref="Option"/> class.
-        /// </summary>
-        /// <param name="aliases">The set of strings that can be used on the command line to specify the option.</param>
-        /// <param name="description">The description of the option shown in help.</param>
-        /// <param name="argumentType">The type that the option's argument(s) can be parsed to.</param>
-        /// <param name="getDefaultValue">A delegate used to get a default value for the option when it is not specified on the command line.</param>
-        /// <param name="arity">The arity of the option.</param>
-        public Option(
-            string[] aliases,
-            string? description = null,
-            Type? argumentType = null,
-            Func<object?>? getDefaultValue = null,
-            ArgumentArity arity = default)
-            : this(aliases, description, CreateArgument(argumentType, getDefaultValue, arity))
-        { }
-
         internal Option(
             string name,
             string? description,

From da4dc4d645e6dba5e214f170d65c63b4bd33218f Mon Sep 17 00:00:00 2001
From: Jon Sequeira <jonsequeira@gmail.com>
Date: Tue, 15 Mar 2022 13:54:20 -0700
Subject: [PATCH 08/11] wip

---
 src/Common/ArgumentBuilder.cs                 | 29 +++++++++++++
 src/Common/OptionBuilder.cs                   | 29 +++++++------
 .../CommandLine.cs                            | 11 ++---
 .../System.CommandLine.DragonFruit.csproj     |  1 +
 .../ModelBinderTests.cs                       | 18 ++------
 ...indingCommandHandlerTests.BindingByName.cs |  6 +--
 .../ModelBindingCommandHandlerTests.cs        | 21 +++-------
 ...ndLine.NamingConventionBinder.Tests.csproj |  1 +
 src/System.CommandLine.Tests/ArgumentTests.cs | 20 ---------
 .../Binding/TypeConversionTests.cs            |  2 +-
 .../Help/HelpBuilderTests.cs                  | 41 +++++++++----------
 .../ParserTests.MultipleArguments.cs          |  6 +--
 .../System.CommandLine.Tests.csproj           |  1 +
 src/System.CommandLine/Argument.cs            |  8 ++--
 src/System.CommandLine/Argument{T}.cs         |  6 +--
 .../Binding/BindingContext.cs                 |  2 +-
 src/System.CommandLine/Option.cs              | 37 +----------------
 17 files changed, 87 insertions(+), 152 deletions(-)
 create mode 100644 src/Common/ArgumentBuilder.cs

diff --git a/src/Common/ArgumentBuilder.cs b/src/Common/ArgumentBuilder.cs
new file mode 100644
index 0000000000..6aa7453862
--- /dev/null
+++ b/src/Common/ArgumentBuilder.cs
@@ -0,0 +1,29 @@
+
+using System;
+using System.CommandLine;
+using System.Reflection;
+
+internal static class ArgumentBuilder
+{
+    private static readonly ConstructorInfo _ctor;
+
+    static ArgumentBuilder()
+    {
+        _ctor = typeof(Argument<string>).GetConstructor(new[] { typeof(string), typeof(string) });
+    }
+
+    public static Argument CreateArgument(Type valueType, string name = "value")
+    {
+        var argumentType = typeof(Argument<>).MakeGenericType(valueType);
+
+#if NET6_0_OR_GREATER
+            var ctor = (ConstructorInfo)argumentType.GetMemberWithSameMetadataDefinitionAs(_ctor);
+#else
+        var ctor = argumentType.GetConstructor(new[] { typeof(string), typeof(string) });
+#endif
+
+        var option = (Argument)ctor.Invoke(new object[] { name, null });
+
+        return option;
+    }
+}
\ No newline at end of file
diff --git a/src/Common/OptionBuilder.cs b/src/Common/OptionBuilder.cs
index d09b2eea60..aafc6df100 100644
--- a/src/Common/OptionBuilder.cs
+++ b/src/Common/OptionBuilder.cs
@@ -3,30 +3,29 @@
 
 using System.Reflection;
 
-namespace System.CommandLine.Utility
+namespace System.CommandLine.Utility;
+
+internal static class OptionBuilder
 {
-    internal static class OptionBuilder
-    {
-        private static readonly ConstructorInfo _ctor;
+    private static readonly ConstructorInfo _ctor;
 
-        static OptionBuilder()
-        {
-            _ctor = typeof(Option<string>).GetConstructor(new[] { typeof(string), typeof(string) });
-        }
+    static OptionBuilder()
+    {
+        _ctor = typeof(Option<string>).GetConstructor(new[] { typeof(string), typeof(string) });
+    }
 
-        public static Option CreateOption(string name, Type valueType)
-        {
-            var optionType = typeof(Option<>).MakeGenericType(valueType);
+    public static Option CreateOption(string name, Type valueType)
+    {
+        var optionType = typeof(Option<>).MakeGenericType(valueType);
 
 #if NET6_0_OR_GREATER
             var ctor = (ConstructorInfo)optionType.GetMemberWithSameMetadataDefinitionAs(_ctor);
 #else
-            var ctor = optionType.GetConstructor(new[] { typeof(string), typeof(string) });
+        var ctor = optionType.GetConstructor(new[] { typeof(string), typeof(string) });
 #endif
 
-            var option = (Option)ctor.Invoke(new object[] { name, null });
+        var option = (Option)ctor.Invoke(new object[] { name, null });
 
-            return option;
-        }
+        return option;
     }
 }
\ No newline at end of file
diff --git a/src/System.CommandLine.DragonFruit/CommandLine.cs b/src/System.CommandLine.DragonFruit/CommandLine.cs
index f8996f0a71..bd73b078ee 100644
--- a/src/System.CommandLine.DragonFruit/CommandLine.cs
+++ b/src/System.CommandLine.DragonFruit/CommandLine.cs
@@ -164,18 +164,13 @@ public static void ConfigureFromMethod(
                 command.AddOption(option);
             }
 
-            if (method.GetParameters()
-                      .FirstOrDefault(p => _argumentParameterNames.Contains(p.Name)) is ParameterInfo argsParam)
+            if (method.GetParameters().FirstOrDefault(p => _argumentParameterNames.Contains(p.Name)) is { } argsParam)
             {
-                var argument = new Argument
-                {
-                    ValueType = argsParam.ParameterType,
-                    Name = argsParam.Name
-                };
+                var argument = ArgumentBuilder.CreateArgument(argsParam.ParameterType, argsParam.Name);
 
                 if (argsParam.HasDefaultValue)
                 {
-                    if (argsParam.DefaultValue != null)
+                    if (argsParam.DefaultValue is not null)
                     {
                         argument.SetDefaultValue(argsParam.DefaultValue);
                     }
diff --git a/src/System.CommandLine.DragonFruit/System.CommandLine.DragonFruit.csproj b/src/System.CommandLine.DragonFruit/System.CommandLine.DragonFruit.csproj
index e67b723ecb..f3fc932610 100644
--- a/src/System.CommandLine.DragonFruit/System.CommandLine.DragonFruit.csproj
+++ b/src/System.CommandLine.DragonFruit/System.CommandLine.DragonFruit.csproj
@@ -14,6 +14,7 @@
   </ItemGroup>
 
   <ItemGroup>
+    <Compile Include="..\Common\ArgumentBuilder.cs" Link="Utility\ArgumentBuilder.cs" />
     <Compile Include="..\Common\OptionBuilder.cs" Link="Utility\OptionBuilder.cs" />
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBinderTests.cs b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBinderTests.cs
index fd4a071b63..cd6c22a608 100644
--- a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBinderTests.cs
+++ b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBinderTests.cs
@@ -58,11 +58,7 @@ public void Command_arguments_are_bound_by_name_to_constructor_parameters(
 
         var command = new Command("the-command")
         {
-            new Argument
-            {
-                Name = "value",
-                ValueType = type
-            }
+            ArgumentBuilder.CreateArgument(type)
         };
 
         var bindingContext = new InvocationContext(command.Parse(commandLine)).BindingContext;
@@ -85,11 +81,7 @@ public void Command_arguments_are_bound_by_name_to_complex_constructor_parameter
 
         var command = new Command("the-command")
         {
-            new Argument
-            {
-                Name = "value",
-                ValueType = type
-            }
+            ArgumentBuilder.CreateArgument(type)
         };
 
         var bindingContext = new InvocationContext(command.Parse(commandLine)).BindingContext;
@@ -164,11 +156,7 @@ public void Command_arguments_are_bound_by_name_to_property_setters(
 
         var command = new Command("the-command")
         {
-            new Argument
-            {
-                Name = "value",
-                ValueType = type
-            }
+            ArgumentBuilder.CreateArgument(type)
         };
         var parser = new Parser(command);
 
diff --git a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.BindingByName.cs b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.BindingByName.cs
index 2e7d9030d1..e3fd786c39 100644
--- a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.BindingByName.cs
+++ b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.BindingByName.cs
@@ -127,11 +127,7 @@ public async Task Command_arguments_are_bound_by_name_to_handler_method_paramete
 
             var command = new Command("the-command")
             {
-                new Argument
-                {
-                    Name = "value",
-                    ValueType = type
-                }
+                ArgumentBuilder.CreateArgument(type)
             };
 
             var console = new TestConsole();
diff --git a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs
index b145b45257..05a0c35ba5 100644
--- a/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs
+++ b/src/System.CommandLine.NamingConventionBinder.Tests/ModelBindingCommandHandlerTests.cs
@@ -165,8 +165,7 @@ public async Task When_binding_fails_due_to_parameter_naming_mismatch_then_handl
     [InlineData(typeof(List<string>))]
     [InlineData(typeof(int[]))]
     [InlineData(typeof(List<int>))]
-    public async Task Handler_method_receives_command_arguments_bound_to_the_specified_type(
-        Type type)
+    public async Task Handler_method_receives_command_arguments_bound_to_the_specified_type(Type type)
     {
         var testCase = BindingCases[type];
 
@@ -176,14 +175,9 @@ public async Task Handler_method_receives_command_arguments_bound_to_the_specifi
 
         var handler = CommandHandler.Create(captureMethod);
 
-        var command = new Command(
-            "command")
+        var command = new Command("command")
         {
-            new Argument
-            {
-                Name = "value",
-                ValueType = testCase.ParameterType
-            }
+            ArgumentBuilder.CreateArgument(type)
         };
         command.Handler = handler;
 
@@ -226,14 +220,9 @@ public async Task Handler_method_receives_command_arguments_explicitly_bound_to_
 
         var handler = CommandHandler.Create(captureMethod);
 
-        var argument = new Argument
-        {
-            Name = "value",
-            ValueType = testCase.ParameterType
-        };
+        var argument = ArgumentBuilder.CreateArgument(testCase.ParameterType, "value");
 
-        var command = new Command(
-            "command")
+        var command = new Command("command")
         {
             argument
         };
diff --git a/src/System.CommandLine.NamingConventionBinder.Tests/System.CommandLine.NamingConventionBinder.Tests.csproj b/src/System.CommandLine.NamingConventionBinder.Tests/System.CommandLine.NamingConventionBinder.Tests.csproj
index 96276ec493..43eb7c29e6 100644
--- a/src/System.CommandLine.NamingConventionBinder.Tests/System.CommandLine.NamingConventionBinder.Tests.csproj
+++ b/src/System.CommandLine.NamingConventionBinder.Tests/System.CommandLine.NamingConventionBinder.Tests.csproj
@@ -14,6 +14,7 @@
   </ItemGroup>
 
   <ItemGroup>
+    <Compile Include="..\Common\ArgumentBuilder.cs" Link="Utility\ArgumentBuilder.cs" />
     <Compile Include="..\Common\OptionBuilder.cs" Link="Utility\OptionBuilder.cs" />
     <Compile Include="..\System.CommandLine.Tests\Binding\TestModels.cs" Link="TestModels.cs" />
     <Compile Include="..\System.CommandLine.Tests\Utility\AssertionExtensions.cs" Link="Utility\AssertionExtensions.cs" />
diff --git a/src/System.CommandLine.Tests/ArgumentTests.cs b/src/System.CommandLine.Tests/ArgumentTests.cs
index 24a7ca1b95..4e27420667 100644
--- a/src/System.CommandLine.Tests/ArgumentTests.cs
+++ b/src/System.CommandLine.Tests/ArgumentTests.cs
@@ -56,26 +56,6 @@ public void When_there_is_no_default_value_then_GetDefaultValue_throws()
                     .Be("Argument \"the-arg\" does not have a default value");
         }
 
-        [Fact]
-        public void When_argument_type_is_set_to_null_then_it_throws()
-        {
-            var argument = new Argument();
-
-            argument.Invoking(a => a.ValueType = null)
-                    .Should()
-                    .Throw<ArgumentNullException>();
-        }
-
-        [Fact]
-        public void By_default_the_argument_type_is_string()
-        {
-            var argument = new Argument();
-
-            argument.ValueType
-                    .Should()
-                    .Be(typeof(string));
-        }
-
         public class CustomParsing
         {
             [Fact]
diff --git a/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs b/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
index 40c6dc49e5..93edfe7959 100644
--- a/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
+++ b/src/System.CommandLine.Tests/Binding/TypeConversionTests.cs
@@ -113,7 +113,7 @@ public void Command_Argument_defaults_arity_to_ZeroOrOne_for_nullable_types()
         [InlineData(typeof(List<int>))]
         public void Argument_infers_arity_of_IEnumerable_types_as_OneOrMore(Type type)
         {
-            var argument = new Argument { ValueType = type };
+            var argument = ArgumentBuilder.CreateArgument(type);
 
             argument.Arity.Should().BeEquivalentTo(ArgumentArity.OneOrMore);
         }
diff --git a/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs b/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
index 573336a6e2..f9693a002c 100644
--- a/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
+++ b/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
@@ -508,9 +508,8 @@ public void Arguments_section_uses_description_if_provided()
         {
             var command = new Command("the-command", "Help text from description")
             {
-                new Argument
+                new Argument<string>
                 {
-                    Arity = ArgumentArity.ExactlyOne,
                     Name = "the-arg",
                     Description = "Help text from HelpDetail"
                 }
@@ -563,7 +562,7 @@ public void Arguments_section_does_not_contain_hidden_argument()
         [Fact]
         public void Arguments_section_does_not_repeat_arguments_that_appear_on_parent_command()
         {
-            var reused = new Argument
+            var reused = new Argument<string>
             {
                 Name = "reused",
                 Description = "This argument is valid on both outer and inner commands"
@@ -621,11 +620,10 @@ public void Arguments_section_keeps_added_newlines()
         {
             var command = new Command("outer", "Help text for the outer command")
             {
-                new Argument
+                new Argument<string>
                 {
                     Name = "outer-command-arg",
-                    Description = $"The argument\r\nfor the\ninner command",
-                    Arity = ArgumentArity.ExactlyOne
+                    Description = $"The argument\r\nfor the\ninner command"
                 }
             };
 
@@ -645,11 +643,10 @@ public void Arguments_section_keeps_added_newlines_when_width_is_very_small()
         {
             var command = new Command("outer", "Help text for the outer command")
             {
-                new Argument
+                new Argument<string>
                 {
                     Name = "outer-command-arg",
                     Description = $"The argument\r\nfor the\ninner command",
-                    Arity = ArgumentArity.ExactlyOne
                 }
             };
 
@@ -678,9 +675,8 @@ public void Arguments_section_properly_wraps_description()
 
             var command = new Command("outer", "Help text for the outer command")
             {
-                new Argument
+                new Argument<string>
                 {
-                    Arity = ArgumentArity.ExactlyOne,
                     Name = "outer-command-arg",
                     Description = longCmdText
                 }
@@ -706,7 +702,7 @@ public void Arguments_section_properly_wraps()
 
             var command = new RootCommand
             {
-                new Argument
+                new Argument<string>
                 {
                     Name = name,
                     Description = description
@@ -727,19 +723,20 @@ public void Arguments_section_properly_wraps()
         }
 
         [Theory]
-        [InlineData(typeof(FileAccess))]
-        [InlineData(typeof(FileAccess?))]
-        public void Command_argument_usage_indicates_enums_values(Type type)
+        [InlineData(true)]
+        [InlineData(false)]
+        public void Command_argument_usage_indicates_enums_values(bool nullable)
         {
             var description = "This is the argument description";
 
+            Argument argument = nullable
+                               ? new Argument<FileAccess?>()
+                               : new Argument<FileAccess>();
+            argument.Description = description;
+
             var command = new Command("outer", "Help text for the outer command")
             {
-                new Argument
-                {
-                    Description = description,
-                    ValueType = type
-                }
+                argument
             };
 
             HelpBuilder helpBuilder = GetHelpBuilder(SmallMaxWidth);
@@ -847,7 +844,7 @@ public void Help_describes_default_value_for_argument()
         [Fact]
         public void Help_does_not_show_default_value_for_argument_when_default_value_is_empty()
         {
-            var argument = new Argument("the-arg", "The argument description");
+            var argument = new Argument<string>("the-arg", "The argument description");
             argument.SetDefaultValue("");
             
             var command = new Command("the-command", "The command description")
@@ -887,12 +884,12 @@ public void Help_does_not_show_default_value_for_option_when_default_value_is_em
         [Fact]
         public void Command_arguments_default_value_provided()
         {
-            var argument = new Argument
+            var argument = new Argument<string>
             {
                 Name = "the-arg",
             };
 
-            var otherArgument = new Argument
+            var otherArgument = new Argument<string>
             {
                 Name = "the-other-arg",
             };
diff --git a/src/System.CommandLine.Tests/ParserTests.MultipleArguments.cs b/src/System.CommandLine.Tests/ParserTests.MultipleArguments.cs
index 01e635ee92..09923bfe64 100644
--- a/src/System.CommandLine.Tests/ParserTests.MultipleArguments.cs
+++ b/src/System.CommandLine.Tests/ParserTests.MultipleArguments.cs
@@ -238,14 +238,12 @@ public void tokens_that_cannot_be_converted_by_multiple_arity_argument_flow_to_n
             [Fact]
             public void Unsatisfied_subsequent_argument_with_min_arity_0_parses_as_default_value()
             {
-                var arg1 = new Argument("arg1")
+                var arg1 = new Argument<string>("arg1")
                 {
-                    ValueType = typeof(string),
                     Arity = ArgumentArity.ExactlyOne
                 };
-                var arg2 = new Argument("arg2")
+                var arg2 = new Argument<string>("arg2")
                 {
-                    ValueType = typeof(string),
                     Arity = ArgumentArity.ZeroOrOne,
                 };
                 arg2.SetDefaultValue("the-default");
diff --git a/src/System.CommandLine.Tests/System.CommandLine.Tests.csproj b/src/System.CommandLine.Tests/System.CommandLine.Tests.csproj
index 955d965fb1..c1988ec497 100644
--- a/src/System.CommandLine.Tests/System.CommandLine.Tests.csproj
+++ b/src/System.CommandLine.Tests/System.CommandLine.Tests.csproj
@@ -29,6 +29,7 @@
   </ItemGroup>
   
   <ItemGroup>
+    <Compile Include="..\Common\ArgumentBuilder.cs" Link="Utility\ArgumentBuilder.cs" />
     <Compile Include="..\Common\OptionBuilder.cs" Link="Utility\OptionBuilder.cs" />
     <Compile Include="..\System.CommandLine.Suggest\DotnetMuxer.cs" Link="Utility\DotnetMuxer.cs" />
   </ItemGroup>
diff --git a/src/System.CommandLine/Argument.cs b/src/System.CommandLine/Argument.cs
index 7ac9603a2b..c86251f88b 100644
--- a/src/System.CommandLine/Argument.cs
+++ b/src/System.CommandLine/Argument.cs
@@ -89,9 +89,8 @@ internal TryConvertArgument? ConvertArguments
         /// </summary>
         public virtual Type ValueType
         {
+            // FIX: (ValueType) make abstract
             get => _valueType;
-
-            set => _valueType = value ?? throw new ArgumentNullException(nameof(value));
         }
 
         private protected override string DefaultName
@@ -182,10 +181,9 @@ public void SetDefaultValueFactory(Func<ArgumentResult, object?> getDefaultValue
 
         internal virtual bool HasCustomParser => false;
 
-        internal static Argument None() => new()
+        internal static Argument None() => new Argument<bool>
         {
-            Arity = ArgumentArity.Zero,
-            ValueType = typeof(bool)
+            Arity = ArgumentArity.Zero
         };
 
         internal void AddAllowedValues(IReadOnlyList<string> values)
diff --git a/src/System.CommandLine/Argument{T}.cs b/src/System.CommandLine/Argument{T}.cs
index 454d906623..1746281d69 100644
--- a/src/System.CommandLine/Argument{T}.cs
+++ b/src/System.CommandLine/Argument{T}.cs
@@ -115,10 +115,6 @@ public Argument(ParseArgument<T> parse, bool isDefault = false) : this(null!, pa
         internal override bool HasCustomParser => _hasCustomParser;
 
         /// <inheritdoc />
-        public override Type ValueType
-        {
-            get => typeof(T);
-            set => throw new NotImplementedException();
-        }
+        public override Type ValueType => typeof(T);
     }
 }
diff --git a/src/System.CommandLine/Binding/BindingContext.cs b/src/System.CommandLine/Binding/BindingContext.cs
index 0bfa6500c3..7f2cbb5ca3 100644
--- a/src/System.CommandLine/Binding/BindingContext.cs
+++ b/src/System.CommandLine/Binding/BindingContext.cs
@@ -100,7 +100,7 @@ internal bool TryBindToScalarValue(
                 else
                 {
                     var parsed = ArgumentConverter.ConvertObject(
-                        valueDescriptor as Argument ?? new Argument(valueDescriptor.ValueName),
+                        valueDescriptor as Argument ?? new Argument<string>(valueDescriptor.ValueName),
                         valueDescriptor.ValueType,
                         value,
                         localizationResources);
diff --git a/src/System.CommandLine/Option.cs b/src/System.CommandLine/Option.cs
index 30dbf7c6cc..e0f4c4e2c2 100644
--- a/src/System.CommandLine/Option.cs
+++ b/src/System.CommandLine/Option.cs
@@ -72,32 +72,7 @@ private void AddArgumentInner(Argument argument)
             argument.AddParent(this);
             _argument = argument;
         }
-
-        private static Argument? CreateArgument(Type? argumentType, Func<object?>? getDefaultValue, ArgumentArity arity)
-        {
-            if (argumentType is null &&
-                getDefaultValue is null &&
-                !arity.IsNonDefault)
-            {
-                return null;
-            }
-
-            var rv = new Argument();
-            if (argumentType is not null)
-            {
-                rv.ValueType = argumentType;
-            }
-            if (getDefaultValue is not null)
-            {
-                rv.SetDefaultValueFactory(getDefaultValue);
-            }
-            if (arity.IsNonDefault)
-            {
-                rv.Arity = arity;
-            }
-            return rv;
-        }
-
+        
         /// <summary>
         /// Gets the <see cref="Argument">argument</see> for the option.
         /// </summary>
@@ -134,15 +109,7 @@ public string? ArgumentHelpName
         public virtual ArgumentArity Arity
         {
             get => Argument.Arity;
-            set
-            {
-                if (value.MaximumNumberOfValues > 0)
-                {
-                    Argument.ValueType = typeof(string);
-                }
-
-                Argument.Arity = value;
-            }
+            set => Argument.Arity = value;
         }
 
         /// <summary>

From 92869432bcff32abd374b42836dbecd136a7b8bf Mon Sep 17 00:00:00 2001
From: Jon Sequeira <jonsequeira@gmail.com>
Date: Tue, 15 Mar 2022 15:10:40 -0700
Subject: [PATCH 09/11] make Argument (non-generic) abstract

---
 src/System.CommandLine.Tests/ArgumentTests.cs |  8 +--
 src/System.CommandLine.Tests/CommandTests.cs  | 14 ++---
 .../CompletionContextTests.cs                 |  5 +-
 .../CompletionTests.cs                        | 14 ++---
 .../Help/HelpBuilderTests.cs                  | 18 +++----
 .../Invocation/TypoCorrectionTests.cs         |  2 +-
 .../ParseResultTests.cs                       |  4 +-
 .../ParserTests.MultipleArguments.cs          | 10 +---
 src/System.CommandLine.Tests/ParserTests.cs   | 54 +++++--------------
 .../ResourceLocalizationTests.cs              | 10 +---
 src/System.CommandLine/Argument.cs            | 16 ++----
 11 files changed, 47 insertions(+), 108 deletions(-)

diff --git a/src/System.CommandLine.Tests/ArgumentTests.cs b/src/System.CommandLine.Tests/ArgumentTests.cs
index 4e27420667..1f4b18aaa1 100644
--- a/src/System.CommandLine.Tests/ArgumentTests.cs
+++ b/src/System.CommandLine.Tests/ArgumentTests.cs
@@ -17,7 +17,7 @@ public class ArgumentTests : SymbolTests
         [Fact]
         public void By_default_there_is_no_default_value()
         {
-            var argument = new Argument();
+            var argument = new Argument<string>();
 
             argument.HasDefaultValue.Should().BeFalse();
         }
@@ -25,7 +25,7 @@ public void By_default_there_is_no_default_value()
         [Fact]
         public void When_default_value_is_set_to_null_then_HasDefaultValue_is_true()
         {
-            var argument = new Argument();
+            var argument = new Argument<string>();
 
             argument.SetDefaultValue(null);
 
@@ -35,7 +35,7 @@ public void When_default_value_is_set_to_null_then_HasDefaultValue_is_true()
         [Fact]
         public void When_default_value_factory_is_set_then_HasDefaultValue_is_true()
         {
-            var argument = new Argument();
+            var argument = new Argument<string[]>();
 
             argument.SetDefaultValueFactory(() => null);
 
@@ -699,7 +699,7 @@ public void OnlyTake_can_pass_on_all_tokens()
 
         protected override Symbol CreateSymbol(string name)
         {
-            return new Argument(name);
+            return new Argument<string>(name);
         }
     }
 }
\ No newline at end of file
diff --git a/src/System.CommandLine.Tests/CommandTests.cs b/src/System.CommandLine.Tests/CommandTests.cs
index 28b3df6c71..04d2f51a60 100644
--- a/src/System.CommandLine.Tests/CommandTests.cs
+++ b/src/System.CommandLine.Tests/CommandTests.cs
@@ -96,18 +96,12 @@ public void Commands_at_multiple_levels_can_have_their_own_arguments()
         {
             var outer = new Command("outer")
             {
-                new Argument
-                {
-                    Arity = ArgumentArity.ExactlyOne
-                }
+                new Argument<string>()
             };
             outer.AddCommand(
                 new Command("inner")
                 {
-                    new Argument
-                    {
-                        Arity = ArgumentArity.ZeroOrMore
-                    }
+                    new Argument<string[]>()
                 });
 
             var parser = new Parser(outer);
@@ -254,9 +248,9 @@ public void It_retains_argument_name_when_it_is_provided()
         {
             var command = new Command("-alias")
             {
-                new Argument
+                new Argument<bool>
                 {
-                    Name = "arg", Arity = ArgumentArity.ZeroOrOne
+                    Name = "arg"
                 }
             };
 
diff --git a/src/System.CommandLine.Tests/CompletionContextTests.cs b/src/System.CommandLine.Tests/CompletionContextTests.cs
index d1a371368c..83dfa3ec35 100644
--- a/src/System.CommandLine.Tests/CompletionContextTests.cs
+++ b/src/System.CommandLine.Tests/CompletionContextTests.cs
@@ -204,10 +204,7 @@ public void When_position_is_specified_in_string_command_line_then_it_returns_ar
             var command =
                 new Command("the-command")
                 {
-                    new Argument
-                    {
-                        Arity = ArgumentArity.ZeroOrMore
-                    }
+                    new Argument<string[]>()
                 };
 
             var position = commandLine.IndexOf("$", StringComparison.Ordinal);
diff --git a/src/System.CommandLine.Tests/CompletionTests.cs b/src/System.CommandLine.Tests/CompletionTests.cs
index 3fdbac7158..cad3b0b9a2 100644
--- a/src/System.CommandLine.Tests/CompletionTests.cs
+++ b/src/System.CommandLine.Tests/CompletionTests.cs
@@ -119,7 +119,7 @@ public void Command_GetCompletions_returns_available_subcommands_and_option_alia
             {
                 new Command("subcommand", "subcommand"),
                 new Option<bool>("--option", "option"),
-                new Argument
+                new Argument<string[]>
                 {
                     Arity = ArgumentArity.OneOrMore,
                     Completions = { "command-argument" }
@@ -156,7 +156,7 @@ public void Command_GetCompletions_does_not_return_argument_names()
         {
             var command = new Command("command")
             {
-                new Argument("the-argument")
+                new Argument<string>("the-argument")
             };
 
             var completions = command.GetCompletions();
@@ -467,10 +467,7 @@ public void Subcommand_names_are_available_as_suggestions()
             {
                 new Command("one", "Command one"),
                 new Command("two", "Command two"),
-                new Argument
-                {
-                    Arity = ArgumentArity.ExactlyOne
-                }
+                new Argument<string>()
             };
 
             var commandLine = "test";
@@ -488,10 +485,7 @@ public void Both_subcommands_and_options_are_available_as_suggestions()
             {
                 new Command("one"),
                 new Option<string>("--one"),
-                new Argument
-                {
-                    Arity = ArgumentArity.ExactlyOne
-                }
+                new Argument<string>()
             };
 
             var commandLine = "test";
diff --git a/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs b/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
index f9693a002c..f21c33965f 100644
--- a/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
+++ b/src/System.CommandLine.Tests/Help/HelpBuilderTests.cs
@@ -127,7 +127,7 @@ public void Usage_section_shows_arguments_if_there_are_arguments_for_command_whe
             int maxArity,
             string expectedArgsUsage)
         {
-            var argument = new Argument
+            var argument = new Argument<string>
             {
                 Name = "the-args",
                 Arity = new ArgumentArity(minArity, maxArity)
@@ -167,14 +167,14 @@ public void Usage_section_shows_arguments_if_there_are_arguments_for_command_whe
             int maxArityForArg2,
             string expectedArgsUsage)
         {
-            var arg1 = new Argument
+            var arg1 = new Argument<string>
             {
                 Name = "arg1",
                 Arity = new ArgumentArity(
                     minArityForArg1,
                     maxArityForArg1)
             };
-            var arg2 = new Argument
+            var arg2 = new Argument<string>
             {
                 Name = "arg2",
                 Arity = new ArgumentArity(
@@ -418,7 +418,7 @@ public void Arguments_section_is_included_if_there_are_commands_with_arguments_c
         {
             var command = new Command("the-command", "command help")
             {
-                new Argument
+                new Argument<string>
                 {
                     Name = "arg command name",
                     Description = "test"
@@ -822,7 +822,7 @@ public void Option_argument_first_column_indicates_enums_values(bool nullable)
         [Fact]
         public void Help_describes_default_value_for_argument()
         {
-            var argument = new Argument
+            var argument = new Argument<string>
             {
                 Name = "the-arg",
                 Description = "Help text from HelpDetail",
@@ -1529,11 +1529,11 @@ public void Subcommand_help_does_not_contain_hidden_argument()
         [Fact]
         public void Help_describes_default_value_for_subcommand_with_arguments_and_only_defaultable_is_shown()
         {
-            var argument = new Argument
+            var argument = new Argument<string>
             {
                 Name = "the-arg",
             };
-            var otherArgumentHidden = new Argument
+            var otherArgumentHidden = new Argument<string>
             {
                 Name = "the-other-hidden-arg",
                 IsHidden = true
@@ -1570,11 +1570,11 @@ public void Help_describes_default_value_for_subcommand_with_arguments_and_only_
         [Fact]
         public void Help_describes_default_values_for_subcommand_with_multiple_defaultable_arguments()
         {
-            var argument = new Argument
+            var argument = new Argument<string>
             {
                 Name = "the-arg",
             };
-            var otherArgument = new Argument
+            var otherArgument = new Argument<string>
             {
                 Name = "the-other-arg"
             };
diff --git a/src/System.CommandLine.Tests/Invocation/TypoCorrectionTests.cs b/src/System.CommandLine.Tests/Invocation/TypoCorrectionTests.cs
index 8223feb1b7..8885eca78f 100644
--- a/src/System.CommandLine.Tests/Invocation/TypoCorrectionTests.cs
+++ b/src/System.CommandLine.Tests/Invocation/TypoCorrectionTests.cs
@@ -124,7 +124,7 @@ public async Task Hidden_commands_are_not_suggested()
         [Fact]
         public async Task Arguments_are_not_suggested()
         {
-            var argument = new Argument("the-argument");
+            var argument = new Argument<string>("the-argument");
             var command = new Command("been");
 
             var parser =
diff --git a/src/System.CommandLine.Tests/ParseResultTests.cs b/src/System.CommandLine.Tests/ParseResultTests.cs
index fef5f791a6..d8f622b630 100644
--- a/src/System.CommandLine.Tests/ParseResultTests.cs
+++ b/src/System.CommandLine.Tests/ParseResultTests.cs
@@ -59,14 +59,14 @@ public void Command_will_not_accept_a_command_if_a_sibling_command_has_already_b
             {
                 new Command("inner-one")
                 {
-                    new Argument
+                    new Argument<bool>
                     {
                         Arity = ArgumentArity.Zero
                     }
                 },
                 new Command("inner-two")
                 {
-                    new Argument
+                    new Argument<bool>
                     {
                         Arity = ArgumentArity.Zero
                     }
diff --git a/src/System.CommandLine.Tests/ParserTests.MultipleArguments.cs b/src/System.CommandLine.Tests/ParserTests.MultipleArguments.cs
index 09923bfe64..9981788ce9 100644
--- a/src/System.CommandLine.Tests/ParserTests.MultipleArguments.cs
+++ b/src/System.CommandLine.Tests/ParserTests.MultipleArguments.cs
@@ -123,14 +123,8 @@ public void When_multiple_arguments_are_present_then_their_order_relative_to_sib
             [Fact]
             public void Multiple_arguments_of_unspecified_type_are_parsed_correctly()
             {
-                var sourceArg = new Argument("source")
-                {
-                    Arity = ArgumentArity.ExactlyOne
-                };
-                var destinationArg = new Argument("destination")
-                {
-                    Arity = ArgumentArity.ExactlyOne
-                };
+                var sourceArg = new Argument<string>("source");
+                var destinationArg = new Argument<string>("destination");
                 var root = new RootCommand
                 {
                     sourceArg,
diff --git a/src/System.CommandLine.Tests/ParserTests.cs b/src/System.CommandLine.Tests/ParserTests.cs
index ed0ba66bf6..429e9f698e 100644
--- a/src/System.CommandLine.Tests/ParserTests.cs
+++ b/src/System.CommandLine.Tests/ParserTests.cs
@@ -185,10 +185,7 @@ public void Options_do_not_get_unbundled_unless_all_resulting_options_would_be_v
             outer.AddOption(new Option<bool>("-a"));
             var inner = new Command("inner")
             {
-                new Argument
-                {
-                    Arity = ArgumentArity.ZeroOrMore
-                }
+                new Argument<string[]>()
             };
             inner.AddOption(new Option<bool>("-b"));
             inner.AddOption(new Option<bool>("-c"));
@@ -390,10 +387,8 @@ public void When_an_option_is_not_respecified_but_limit_is_reached_then_the_foll
                 {
                     animalsOption,
                     vegetablesOption,
-                    new Argument
-                    {
-                        Arity = ArgumentArity.ZeroOrMore
-                    }});
+                    new Argument<string[]>()
+                });
 
             var result = parser.Parse("the-command -a cat some-arg -v carrot");
 
@@ -541,16 +536,10 @@ public void When_nested_commands_all_accept_arguments_then_the_nearest_captures_
             var command = new Command(
                 "outer")
             {
-                new Argument
-                {
-                    Arity = ArgumentArity.ZeroOrMore
-                },
+                new Argument<string[]>(),
                 new Command("inner")
                 {
-                    new Argument
-                    {
-                        Arity = ArgumentArity.ZeroOrMore
-                    }
+                    new Argument<string[]>()
                 }
             };
 
@@ -848,10 +837,7 @@ public void Absolute_unix_style_paths_are_lexed_correctly()
 
             var parser = new Parser(new Command("rm")
             {
-                new Argument
-                {
-                    Arity = ArgumentArity.ZeroOrMore
-                }
+                new Argument<string[]>()
             });
 
             var result = parser.Parse(command);
@@ -871,10 +857,7 @@ public void Absolute_Windows_style_paths_are_lexed_correctly()
 
             var parser = new Parser(new Command("rm")
             {
-                new Argument
-                {
-                    Arity = ArgumentArity.ZeroOrMore
-                }
+                new Argument<string[]>()
             });
 
             ParseResult result = parser.Parse(command);
@@ -1021,10 +1004,7 @@ public void The_default_behavior_of_unmatched_tokens_resulting_in_errors_can_be_
         {
             var command = new Command("the-command")
             {
-                new Argument
-                {
-                    Arity = ArgumentArity.ExactlyOne
-                }
+                new Argument<string>()
             };
             command.TreatUnmatchedTokensAsErrors = false;
 
@@ -1410,7 +1390,7 @@ public void Parse_can_be_called_with_null_args()
         [Fact]
         public void Command_argument_arity_can_be_a_fixed_value_greater_than_1()
         {
-            var argument = new Argument
+            var argument = new Argument<string[]>
             {
                 Arity = new ArgumentArity(3, 3)
             };
@@ -1432,7 +1412,7 @@ public void Command_argument_arity_can_be_a_fixed_value_greater_than_1()
         [Fact]
         public void Command_argument_arity_can_be_a_range_with_a_lower_bound_greater_than_1()
         {
-            var argument = new Argument
+            var argument = new Argument<string[]>
             {
                 Arity = new ArgumentArity(3, 5)
             };
@@ -1466,7 +1446,7 @@ public void When_command_arguments_are_fewer_than_minimum_arity_then_an_error_is
         {
             var command = new Command("the-command")
             {
-                new Argument
+                new Argument<string[]>
                 {
                     Arity = new ArgumentArity(2, 3)
                 }
@@ -1485,7 +1465,7 @@ public void When_command_arguments_are_greater_than_maximum_arity_then_an_error_
         {
             var command = new Command("the-command")
             {
-                new Argument
+                new Argument<string[]>
                 {
                     Arity = new ArgumentArity(2, 3)
                 }
@@ -1605,15 +1585,9 @@ public void A_subcommand_wont_overflow_when_checking_maximum_argument_capcity()
         {
             // Tests bug identified in https://github.com/dotnet/command-line-api/issues/997
 
-            var argument1 = new Argument("arg1")
-            {
-                Arity = ArgumentArity.ExactlyOne
-            };
+            var argument1 = new Argument<string>("arg1");
 
-            var argument2 = new Argument<string[]>("arg2")
-            {
-                Arity = ArgumentArity.OneOrMore
-            };
+            var argument2 = new Argument<string[]>("arg2");
 
             var command = new Command("subcommand")
             {
diff --git a/src/System.CommandLine.Tests/ResourceLocalizationTests.cs b/src/System.CommandLine.Tests/ResourceLocalizationTests.cs
index e4d6749a01..0504d86e3d 100644
--- a/src/System.CommandLine.Tests/ResourceLocalizationTests.cs
+++ b/src/System.CommandLine.Tests/ResourceLocalizationTests.cs
@@ -19,10 +19,7 @@ public void Default_validation_messages_can_be_replaced_in_order_to_add_localiza
 
             var command = new Command("the-command")
             {
-                new Argument
-                {
-                    Arity = ArgumentArity.ExactlyOne
-                }
+                new Argument<string>()
             };
             var parser = new Parser(new CommandLineConfiguration(command, resources: messages));
             var result = parser.Parse("the-command");
@@ -40,10 +37,7 @@ public void Default_validation_messages_can_be_replaced_using_CommandLineBuilder
 
             var parser = new CommandLineBuilder(new Command("the-command")
                          {
-                             new Argument
-                             {
-                                 Arity = ArgumentArity.ExactlyOne
-                             }
+                             new Argument<string>()
                          })
                          .UseLocalizationResources(messages)
                          .Build();
diff --git a/src/System.CommandLine/Argument.cs b/src/System.CommandLine/Argument.cs
index c86251f88b..8cdce978a8 100644
--- a/src/System.CommandLine/Argument.cs
+++ b/src/System.CommandLine/Argument.cs
@@ -12,23 +12,19 @@ namespace System.CommandLine
     /// <summary>
     /// A symbol defining a value that can be passed on the command line to a <see cref="Command">command</see> or <see cref="Option">option</see>.
     /// </summary>
-    public class Argument : Symbol, IValueDescriptor
+    public abstract class Argument : Symbol, IValueDescriptor
     {
         private Func<ArgumentResult, object?>? _defaultValueFactory;
         private ArgumentArity _arity;
         private TryConvertArgument? _convertArguments;
-
-        private Type _valueType = typeof(string);
-        
         private CompletionSourceList? _completions = null;
         private List<ValidateSymbolResult<ArgumentResult>>? _validators = null;
 
         /// <summary>
         /// Initializes a new instance of the Argument class.
         /// </summary>
-        public Argument()
+        protected Argument()
         {
-            // FIX: (Argument) make this protected
         }
 
         /// <summary>
@@ -36,7 +32,7 @@ public Argument()
         /// </summary>
         /// <param name="name">The name of the argument.</param>
         /// <param name="description">The description of the argument, shown in help.</param>
-        public Argument(string? name = null, string? description = null)
+        protected Argument(string? name = null, string? description = null)
         {
             Name = name!;
             Description = description;
@@ -87,11 +83,7 @@ internal TryConvertArgument? ConvertArguments
         /// <summary>
         /// Gets or sets the <see cref="Type" /> that the argument token(s) will be converted to.
         /// </summary>
-        public virtual Type ValueType
-        {
-            // FIX: (ValueType) make abstract
-            get => _valueType;
-        }
+        public abstract Type ValueType { get; }
 
         private protected override string DefaultName
         {

From 20577804b4ae2edb9451044c51335d46e9fa7f33 Mon Sep 17 00:00:00 2001
From: Jon Sequeira <jonsequeira@gmail.com>
Date: Tue, 15 Mar 2022 16:35:01 -0700
Subject: [PATCH 10/11] cleanup

---
 .../ModelBindingCommandHandler.cs             |  1 +
 .../Binding/ArgumentConverter.cs              | 49 ++++++-------------
 src/System.CommandLine/Option.cs              | 37 +++-----------
 src/System.CommandLine/Option{T}.cs           |  2 +-
 4 files changed, 23 insertions(+), 66 deletions(-)

diff --git a/src/System.CommandLine.NamingConventionBinder/ModelBindingCommandHandler.cs b/src/System.CommandLine.NamingConventionBinder/ModelBindingCommandHandler.cs
index 292e545de9..05ca904a33 100644
--- a/src/System.CommandLine.NamingConventionBinder/ModelBindingCommandHandler.cs
+++ b/src/System.CommandLine.NamingConventionBinder/ModelBindingCommandHandler.cs
@@ -129,5 +129,6 @@ private void BindValueSource(ParameterInfo param, IValueSource valueSource)
                                   .FirstOrDefault(x => x.ValueName == param.Name &&
                                                        x.ValueType == param.ParameterType);
 
+    /// <inheritdoc />
     public int Invoke(InvocationContext context) => InvokeAsync(context).GetAwaiter().GetResult();
 }
\ No newline at end of file
diff --git a/src/System.CommandLine/Binding/ArgumentConverter.cs b/src/System.CommandLine/Binding/ArgumentConverter.cs
index 5207304f0d..bc86831770 100644
--- a/src/System.CommandLine/Binding/ArgumentConverter.cs
+++ b/src/System.CommandLine/Binding/ArgumentConverter.cs
@@ -76,18 +76,7 @@ private static ArgumentConversionResult ConvertTokens(
             LocalizationResources localizationResources,
             ArgumentResult? argumentResult = null)
         {
-            Type itemType;
-
-            if (type == typeof(string))
-            {
-                type = typeof(string[]);
-                itemType = typeof(string);
-            }
-            else
-            {
-                itemType = type.GetElementTypeIfEnumerable() ?? typeof(string);
-            }
-
+            var itemType = type.GetElementTypeIfEnumerable() ?? typeof(string);
             var values = CreateEnumerable(type, itemType, tokens.Count);
             var isArray = values is Array;
 
@@ -99,9 +88,6 @@ private static ArgumentConversionResult ConvertTokens(
 
                 switch (result.Result)
                 {
-                    case ArgumentConversionResultType.NoArgument:
-                        break;
-
                     case ArgumentConversionResultType.Successful:
                         if (isArray)
                         {
@@ -132,25 +118,21 @@ private static ArgumentConversionResult ConvertTokens(
 
         internal static TryConvertArgument? GetConverter(Argument argument)
         {
-            switch (argument.Arity)
+            if (argument.Arity is { MaximumNumberOfValues: 1, MinimumNumberOfValues: 1 })
             {
-                case { MaximumNumberOfValues: 1, MinimumNumberOfValues: 1 }:
-
-                    if (argument.ValueType.TryGetNullableType(out var nullableType) &&
-                        _stringConverters.TryGetValue(nullableType, out var convertNullable))
-                    {
-                        return (ArgumentResult result, out object? value) => ConvertSingleString(result, convertNullable, out value);
-                    }
-
-                    if (_stringConverters.TryGetValue(argument.ValueType, out var convert))
-                    {
-                        return (ArgumentResult result, out object? value) => ConvertSingleString(result, convert, out value);
-                    }
+                if (argument.ValueType.TryGetNullableType(out var nullableType) &&
+                    _stringConverters.TryGetValue(nullableType, out var convertNullable))
+                {
+                    return (ArgumentResult result, out object? value) => ConvertSingleString(result, convertNullable, out value);
+                }
 
-                    static bool ConvertSingleString(ArgumentResult result, TryConvertString convert, out object? value) =>
-                        convert(result.Tokens[result.Tokens.Count - 1].Value, out value);
+                if (_stringConverters.TryGetValue(argument.ValueType, out var convert1))
+                {
+                    return (ArgumentResult result, out object? value) => ConvertSingleString(result, convert1, out value);
+                }
 
-                    break;
+                static bool ConvertSingleString(ArgumentResult result, TryConvertString convert, out object? value) =>
+                    convert(result.Tokens[result.Tokens.Count - 1].Value, out value);
             }
 
             if (argument.ValueType.CanBeBoundFromScalarValue())
@@ -215,10 +197,7 @@ internal static ArgumentConversionResult ConvertIfNeeded(
                         conversionResult.Argument,
                         symbolResult.LocalizationResources.RequiredArgumentMissing(symbolResult),
                         ArgumentConversionResultType.FailedMissingArgument),
-
-                ArgumentConversionResultType.NoArgument when conversionResult.Argument.Arity.MaximumNumberOfValues > 1 =>
-                    Success(conversionResult.Argument, Array.Empty<string>()),
-
+                        
                 _ => conversionResult
             };
         }
diff --git a/src/System.CommandLine/Option.cs b/src/System.CommandLine/Option.cs
index e0f4c4e2c2..9f17f0242f 100644
--- a/src/System.CommandLine/Option.cs
+++ b/src/System.CommandLine/Option.cs
@@ -17,12 +17,12 @@ public abstract class Option : IdentifierSymbol, IValueDescriptor
     {
         private string? _name;
         private List<ValidateSymbolResult<OptionResult>>? _validators;
-        private Argument? _argument;
+        private readonly Argument _argument;
 
         internal Option(
             string name,
             string? description,
-            Argument? argument)
+            Argument argument)
             : base(description)
         {
             if (name is null)
@@ -34,16 +34,14 @@ internal Option(
 
             AddAlias(name);
 
-            if (argument is not null)
-            {
-                AddArgumentInner(argument);
-            }
+            argument.AddParent(this);
+            _argument = argument;
         }
 
         internal Option(
             string[] aliases,
             string? description,
-            Argument? argument)
+            Argument argument)
             : base(description)
         {
             if (aliases is null)
@@ -61,35 +59,14 @@ internal Option(
                 AddAlias(aliases[i]);
             }
 
-            if (argument is not null)
-            {
-                AddArgumentInner(argument);
-            }
-        }
-
-        private void AddArgumentInner(Argument argument)
-        {
             argument.AddParent(this);
             _argument = argument;
         }
-        
+
         /// <summary>
         /// Gets the <see cref="Argument">argument</see> for the option.
         /// </summary>
-        internal virtual Argument Argument
-        {
-            get
-            {
-                if (_argument is null)
-                {
-                    var none = Argument.None();
-                    none.AddParent(this);
-                    _argument = none;
-                }
-
-                return _argument;
-            }
-        }
+        internal virtual Argument Argument => _argument;
 
         /// <summary>
         /// Gets or sets the name of the argument when displayed in help.
diff --git a/src/System.CommandLine/Option{T}.cs b/src/System.CommandLine/Option{T}.cs
index 0d890c814b..5b049a42f0 100644
--- a/src/System.CommandLine/Option{T}.cs
+++ b/src/System.CommandLine/Option{T}.cs
@@ -6,7 +6,7 @@
 
 namespace System.CommandLine
 {
-    /// <inheritdoc/>
+    /// <inheritdoc cref="Option" />
     /// <typeparam name="T">The <see cref="System.Type"/> that the option's arguments are expected to be parsed as.</typeparam>
     public class Option<T> : Option, IValueDescriptor<T>
     {

From 78a9e1a83adafddcd203b4c2a1739dc92fb780fb Mon Sep 17 00:00:00 2001
From: Jon Sequeira <jonsequeira@gmail.com>
Date: Wed, 16 Mar 2022 09:01:23 -0700
Subject: [PATCH 11/11] update API test baseline

---
 ...stem_CommandLine_api_is_not_changed.approved.txt | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt b/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
index 6ffedb9684..32365a95ab 100644
--- a/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
+++ b/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
@@ -1,12 +1,10 @@
 System.CommandLine
-  public class Argument : Symbol, System.CommandLine.Binding.IValueDescriptor, System.CommandLine.Completions.ICompletionSource
-    .ctor()
-    .ctor(System.String name = null, System.String description = null)
+  public abstract class Argument : Symbol, System.CommandLine.Binding.IValueDescriptor, System.CommandLine.Completions.ICompletionSource
     public ArgumentArity Arity { get; set; }
     public CompletionSourceList Completions { get; }
     public System.Boolean HasDefaultValue { get; }
     public System.String HelpName { get; set; }
-    public System.Type ValueType { get; set; }
+    public System.Type ValueType { get; }
     public System.Void AddValidator(System.CommandLine.Parsing.ValidateSymbolResult<System.CommandLine.Parsing.ArgumentResult> validate)
     public System.Collections.Generic.IEnumerable<System.CommandLine.Completions.CompletionItem> GetCompletions(System.CommandLine.Completions.CompletionContext context)
     public System.Object GetDefaultValue()
@@ -21,7 +19,7 @@
     .ctor(Func<T> getDefaultValue)
     .ctor(System.String name, ParseArgument<T> parse, System.Boolean isDefault = False, System.String description = null)
     .ctor(ParseArgument<T> parse, System.Boolean isDefault = False)
-    public System.Type ValueType { get; set; }
+    public System.Type ValueType { get; }
   public struct ArgumentArity : System.ValueType, System.IEquatable<ArgumentArity>
     public static ArgumentArity ExactlyOne { get; }
     public static ArgumentArity OneOrMore { get; }
@@ -181,10 +179,7 @@
     public System.String UnrecognizedCommandOrArgument(System.String arg)
     public System.String VersionOptionCannotBeCombinedWithOtherArguments(System.String optionAlias)
     public System.String VersionOptionDescription()
-  public class Option : IdentifierSymbol, System.CommandLine.Binding.IValueDescriptor, System.CommandLine.Completions.ICompletionSource
-    .ctor(System.String name)
-    .ctor(System.String name, System.String description = null, System.Type argumentType = null, System.Func<System.Object> getDefaultValue = null, ArgumentArity arity = null)
-    .ctor(System.String[] aliases, System.String description = null, System.Type argumentType = null, System.Func<System.Object> getDefaultValue = null, ArgumentArity arity = null)
+  public abstract class Option : IdentifierSymbol, System.CommandLine.Binding.IValueDescriptor, System.CommandLine.Completions.ICompletionSource
     public System.Boolean AllowMultipleArgumentsPerToken { get; set; }
     public System.String ArgumentHelpName { get; set; }
     public ArgumentArity Arity { get; set; }