ScriptableRenderPipeline/UnityProject/Assets/Editor/Material/Nodes/Extensions.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace UnityEditor.Graphs.Material
{
	internal static class Extensions
	{
		public static IEnumerable<TSource> Except<TSource>(this IEnumerable<TSource> first, 
															IEnumerable<TSource> second , Func<TSource, TSource, bool> comparer )
		{
			return first.Except(second, new LambdaComparer<TSource>(comparer));
		}

		public class LambdaComparer<T> : IEqualityComparer<T>
		{
			private readonly Func<T, T, bool> _lambdaComparer;
			private readonly Func<T, int> _lambdaHash;

			public LambdaComparer(Func<T, T, bool> lambdaComparer) :
				this(lambdaComparer, o => 0)
			{
			}
    
			public LambdaComparer(Func<T, T, bool> lambdaComparer, Func<T, int> lambdaHash)
			{
				if (lambdaComparer == null)
					throw new ArgumentNullException("lambdaComparer");
				if (lambdaHash == null)
					throw new ArgumentNullException("lambdaHash");

				_lambdaComparer = lambdaComparer;
				_lambdaHash = lambdaHash;
			}

			public bool Equals(T x, T y)
			{
				return _lambdaComparer(x, y);
			}

			public int GetHashCode(T obj)
			{
				return _lambdaHash(obj);
			}
		}
	}
}