C# Records

This Visual Studio extension will propose a code fix on classes that use public readonly fields or properties. Applying this code fix will generate or update both the constructor, and a F# inspired "With" update method.

public class Foo
{
    public string First { get; }
    public int Second { get; }
}

would be updated to

public class Foo
{
    public string First { get; }
    public int Second { get; }

    public Foo(string First, int Second)
    {
        this.First = First;
        this.Second = Second;
    }

    public Foo With(string First = null, int? Second)
    {
        return new Foo(First ?? this.First, Second ?? this.Second);
    }
}

Non nullable types and the With method

When generating the With method, the extension will automatically use the nullable type syntax on applicable predefined types like int or bool, and on widely used struct types like System.Guid and System.DateTime. Unfortunately, a basic AST level analysis can't reveal all struct types: you may need to manually and the ? at the end of a parameter type. All subsequent use of the code fix will use the hint that this parameter type is non nullable.

Known limitations

The implementation of the With method implies that a field cannot be set to null using it : it will default to the value of the previous instance.