LambdaComparer.cs

    public static class LambdaComparer
    {

        /// <summary>
        /// Creates an <see cref="IEqualityComparer&lt;T&gt;"/> using the given <paramref name="equalsFunc"/> and a constant <see cref="IEqualityComparer&lt;T&gt;.GetHashCode(T)"/> function.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="equalsFunc">A function to use for <see cref="IEqualityComparer&lt;T&gt;.Equals(T, T)"/></param>
        /// <returns>An <see cref="IEqualityComparer&lt;T&gt;"/></returns>
        /// <remarks>Since <see cref="IEqualityComparer&lt;T&gt;.GetHashCode(T)"/> will be constant, this comparer will not perform well on large sets.  For performance
        /// critical code, use <see cref="Create&lt;T&gt;(Func&lt;T, T, bool&gt;, Func&lt;T, int&gt;)"/></remarks>
        public static IEqualityComparer<T> Create<T>(Func<T, T, bool> equalsFunc)
        {
            return Create(equalsFunc, o => 0);
        }

        /// <summary>
        /// Creates an <see cref="IEqualityComparer&lt;T&gt;"/> using the given <paramref name="equalsFunc"/> and <paramref name="hashCodeFunc"/>
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="equalsFunc">A function to use for <see cref="IEqualityComparer&lt;T&gt;.Equals(T, T)"/></param>
        /// <param name="hashCodeFunc">A function to use for <see cref="IEqualityComparer&lt;T&gt;.GetHashCode(T)"/></param>
        /// <returns>An <see cref="IEqualityComparer&lt;T&gt;"/></returns>
        public static IEqualityComparer<T> Create<T>(Func<T, T, bool> equalsFunc, Func<T, int> hashCodeFunc)
        {
            return new LambdaComparer<T>(equalsFunc, hashCodeFunc);
        } 
    }

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

        public LambdaComparer(Func<T, T, bool> equalsFunc, Func<T, int> hashCodeFunc)
        {
            _equalsFunc = equalsFunc;
            _hashCodeFunc = hashCodeFunc;
        }

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

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