Constraint weirdness

TheGreatWeirdness.cs

using System;
using System.Linq;
using System.Linq.Expressions;

namespace TheGreatWeirdness
{
	public interface IKeyHolder
	{
		string Key { get; }
	}

	public static class ExpressionGenerator<T> where T : IKeyHolder
	{
		public static Expression<Func<T, bool>> CreateWhereExpression( string[] values )
		{
			return ( T item ) => values.Contains( item.Key );
		}
	}

	public class KeyHolder : IKeyHolder
	{
		public string Key => "42";
	}

	class Program
	{
		static void Main( string[] args )
		{
			Expression expr = ExpressionGenerator<KeyHolder>.CreateWhereExpression( Array.Empty<string>() );
			Console.WriteLine( expr.ToString() );
		}
	}
}

/* The output:

item => value(TheGreatWeirdness.ExpressionGenerator`1+<>c__DisplayClass0_0[TheGreatWeirdness.KeyHolder]).values.Contains(Convert(item).Key)
*/