No value or parsing error if [Option] arg equals to [Value] arg

[zii-dmg]

Example:

class SameOptionAndPosValueArgs
{
	[Option('u', "unit")]
	public string OptValue{get; set}

	[Value(0)]
	public string PosValue{get; set}
}

[Fact]
public void SameOptionAndPosValue()
{
	var parser = Parser.Default;
	var result = parser.ParseArguments<SameOptionAndPosValueArgs>(
		new[]{"arg", "-u", "arg" }); // !!! pos and value are "arg"
	result
		.WithNotParsed(errors =>{throw new InvalidOperationException("Must be parsed.")})
		.WithParsed(args =>
		{
			Assert.Equal("arg", args.OptValue);
			Assert.Equal("arg", args.PosValue); // !!! args.PosValue is null
		});
}

When user enters same values for [Option] and [Value] args, parser is losing one of it because they are equal tokens.

TokenPartitioner.cs has code:

var nonOptions = tokenList
 .Where(t => !switches.Contains(t))
 .Where(t => !scalars.Contains(t))
 .Where(t => !sequences.Contains(t)).Memorize();
var values = nonOptions.Where(v => v.IsValue()).Memorize();
var errors = nonOptions.Except(values).Memorize();

One of tokens for "-u" option is already in scalars variable so Where is filtering out both tokens with "arg" and then its not gettings into values. Filtering is happening because all tokens classes have IEqualtable<T> so "arg" == "arg" but it is two different items in memory.

One of solutions: make reference comparing, not IEqutable<T>. .Net doesn't have such comparer. Stackoverflow helps:

internal sealed class ReferenceEqualityComparer : IEqualityComparer, IEqualityComparer<object>
{
	public static readonly ReferenceEqualityComparer Default = new ReferenceEqualityComparer();

	public new bool Equals(object x, object y)
	{
		return x == y; // reference equality because operator== is static and resolved at compile-time
	}

	public int GetHashCode(object obj)
	{
		return RuntimeHelpers.GetHashCode(obj);
	}
}

Pass this comparer to Contains and Except:

var nonOptions = tokenList
	.Where(t => !switches.Contains(t, ReferenceEqualityComparer.Default))
	.Where(t => !scalars.Contains(t, ReferenceEqualityComparer.Default))
	.Where(t => !sequences.Contains(t, ReferenceEqualityComparer.Default)).Memorize();
var values = nonOptions.Where(v => v.IsValue()).Memorize();
var errors = nonOptions.Except(values, ReferenceEqualityComparer.Default).Cast<Token>().Memorize();

[nemec]

Hi @zii-dmg I think you have a good plan there. Would you mind submitting a pull request with your solution + test? If all the tests pass, I'll get it merged.

[zii-dmg]

Just a note: some tests failing if I have not default size cmd window. Different word wrapping.
Also I have to remove project.json for tests project to compile.