Add support for guid options

src/CommandLineUtils/Abstractions/DefaultValueParserFactory.cs

@@ -0,0 +1,123 @@
+namespace McMaster.Extensions.CommandLineUtils.Abstractions
+{
+    using System;
+    using System.Collections.Generic;
+    using System.ComponentModel;
+    using System.Diagnostics;
+    using System.Globalization;
+    using System.Text;
+
+    /// <summary>
+    /// A factory creating generic implementations of <see cref="IValueParser{T}"/>. The implementations are based
+    /// on automatically located <see cref="TypeConverter"/> classes that are suitable for parsing.
+    /// </summary>
+    sealed class DefaultValueParserFactory
+    {
+        const int DefaultMaxCacheCapacity = 100;
+
+        #region Private Fields
+
+        private readonly int _maxCacheCapacity;
+
+        [DebuggerBrowsable(DebuggerBrowsableState.RootHidden)]
+        readonly Dictionary<Type, IValueParser> _parsersByTargetType = new Dictionary<Type, IValueParser>();
+
+        [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+        readonly HashSet<Type> _notSupportedTypes = new HashSet<Type>();
+
+        #endregion
+
+        public DefaultValueParserFactory(int maxCacheCapacity = DefaultMaxCacheCapacity)
+        {
+            _maxCacheCapacity = maxCacheCapacity;
+            if (_maxCacheCapacity < 1) throw new ArgumentOutOfRangeException(nameof(maxCacheCapacity));
+        }
+
+        [DebuggerStepThrough]
+        public bool TryGetParser<T>(out IValueParser<T> parser)
+        {
+            if (TryGetParser<T>(out IValueParser generalizedParser))
+            {
+                parser = (IValueParser<T>)generalizedParser;
+                return true;
+            }
+
+            parser = null;
+            return false;
+        }
+
+        public bool TryGetParser<T>(out IValueParser parser)
+        {
+            var targetType = typeof(T);
+            if (_notSupportedTypes.Contains(targetType))
+            {
+                parser = null;
+                return false;
+            }
+
+            if (_parsersByTargetType.TryGetValue(targetType, out parser))
+            {
+                Debug.Assert(targetType == parser.TargetType);
+                return true;
+            }
+
+            var converter = TypeDescriptor.GetConverter(targetType);
+            if (converter.CanConvertFrom(typeof(string)))
+            {
+                if (_parsersByTargetType.Count >= _maxCacheCapacity)
+                    _parsersByTargetType.Clear();
+                parser = new TypeConverterValueParser<T>(targetType, converter);
+                _parsersByTargetType[targetType] = parser;
+                Debug.Assert(_parsersByTargetType.Count <= _maxCacheCapacity);
+                return true;
+            }
+
+            parser = null;
+            if (_notSupportedTypes.Count > _maxCacheCapacity)
+                _notSupportedTypes.Clear();
+            _notSupportedTypes.Add(targetType);
+            Debug.Assert(_notSupportedTypes.Count <= _maxCacheCapacity);
+            return false;
+        }
+
+        public IValueParser<T> GetParser<T>()
+        {
+            return TryGetParser<T>(out IValueParser<T> converter)
+                ? converter
+                : throw new NotSupportedException(
+                    new StringBuilder($"No suitable type converter found for {typeof(T)}.")
+                        .Append($" Make sure a type converter capable of parsing {typeof(string)} to {typeof(T)} exists and is discoverable.")
+                        .Append($" Did you forget to annotate the target type with {typeof(TypeConverterAttribute)}?")
+                        .ToString());
+        }
+
+        private sealed class TypeConverterValueParser<T> : IValueParser<T>
+        {
+            public TypeConverterValueParser(Type targetType, TypeConverter typeConverter)
+            {
+                TargetType = targetType ?? throw new ArgumentNullException(nameof(targetType));
+                TypeConverter = typeConverter ?? throw new ArgumentNullException(nameof(typeConverter));
+            }
+
+            public Type TargetType { get; }
+
+            private TypeConverter TypeConverter { get; }
+
+            public T Parse(string argName, string value, CultureInfo culture)
+            {
+                try
+                {
+                    culture ??= CultureInfo.InvariantCulture;
+                    return (T)TypeConverter.ConvertFromString(null, culture, value);
+                }
+                catch (ArgumentException e)
+                {
+                    throw new FormatException(e.Message, e);
+                }
+            }
+
+            object IValueParser.Parse(string argName, string value, CultureInfo culture) => Parse(argName, value, culture);
+        }
+
+    }
+}

src/CommandLineUtils/Abstractions/ValueParserProvider.cs

@@ -15,6 +15,7 @@ namespace McMaster.Extensions.CommandLineUtils.Abstractions
     public class ValueParserProvider
     {
         private readonly Dictionary<Type, IValueParser> _parsers = new Dictionary<Type, IValueParser>(10);
+        private readonly DefaultValueParserFactory _defaultValueParserFactory = new DefaultValueParserFactory();
 
         internal ValueParserProvider()
         {
@@ -100,6 +101,9 @@ public IValueParser GetParser(Type type)
                 return EnumParser.Create(type);
             }
 
+            if (_defaultValueParserFactory.TryGetParser<T>(out parser))
+                return parser;
+
             if (ReflectionHelper.IsNullableType(type, out var wrappedType) && wrappedType != null)
             {
                 if (wrappedType.IsEnum)

test/CommandLineUtils.Tests/ValueParserProviderTests.cs

@@ -110,6 +110,12 @@ private class Program
 
             [Option("--timespan")]
             public TimeSpan TimeSpan { get; }
+
+            [Option("--guid", CommandOptionType.SingleValue)]
+            public Guid Guid { get; }
+
+            [Option("--guid-opt", CommandOptionType.SingleValue)]
+            public Guid? GuidOpt { get; }
         }
 
         private sealed class InCulture : IDisposable
@@ -480,6 +486,35 @@ public void ParsesBoolArray(int repeat)
             Assert.All(parsed.Flags, value => Assert.True(value));
         }
 
+        [Theory]
+        [InlineData("ff23ef12-500a-48df-9a5d-151c2adc2a0a")]
+        [InlineData("ff23ef12500a48df9a5d151c2adc2a0a")]
+        [InlineData("{ff23ef12-500a-48df-9a5d-151c2adc2a0a}")]
+        [InlineData("(ff23ef12-500a-48df-9a5d-151c2adc2a0a)")]
+        [InlineData("{0xff23ef12,0x500a,0x48df,{0x9a,0x5d,0x15,0x1c,0x2a,0xdc,0x2a,0x0a}}")]
+        public void ParsesGuid(string arg)
+        {
+            var expected = Guid.Parse("ff23ef12-500a-48df-9a5d-151c2adc2a0a");
+            var parsed = CommandLineParser.ParseArgs<Program>("--guid", arg);
+            Assert.Equal(expected, parsed.Guid);
+        }
+
+        [Theory]
+        [InlineData("ff23ef12-500a-48df-9a5d-151c2adc2a0a")]
+        [InlineData("ff23ef12500a48df9a5d151c2adc2a0a")]
+        [InlineData("{ff23ef12-500a-48df-9a5d-151c2adc2a0a}")]
+        [InlineData("(ff23ef12-500a-48df-9a5d-151c2adc2a0a)")]
+        [InlineData("{0xff23ef12,0x500a,0x48df,{0x9a,0x5d,0x15,0x1c,0x2a,0xdc,0x2a,0x0a}}")]
+        [InlineData("")]
+        public void ParsesGuidNullable(string arg)
+        {
+            var expected = String.IsNullOrWhiteSpace(arg)
+                ? (Guid?)null
+                : Guid.Parse("ff23ef12-500a-48df-9a5d-151c2adc2a0a");
+            var parsed = CommandLineParser.ParseArgs<Program>("--guid-opt", arg);
+            Assert.Equal(expected, parsed.GuidOpt);
+        }
+
         [Theory]
         [InlineData(nameof(Program.Float), "--float", "123.456,7", "de-DE", 123456.7f)]
         [InlineData(nameof(Program.Double), "--double", "123.456,789", "de-DE", 123456.789)]