using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var comparer = new GenericComparer<DateTime>(

                (dateA, dateB) => dateA.ToString("ddMMyyyy").Equals(dateB.ToString("ddMMyyyy")),

                (date) => {throw new NotImplementedException();});

​

            Console.WriteLine(comparer.Equals(new DateTime(2019, 01, 01), new DateTime(2019, 01, 01)));

            Console.WriteLine(comparer.Equals(new DateTime(2019, 01, 01), new DateTime(2019, 01, 02)));

            Console.WriteLine(comparer.Equals(new DateTime(2019, 01, 01), new DateTime(2019, 02, 02)));

            Console.WriteLine(comparer.Equals(new DateTime(2019, 01, 01), new DateTime(2018, 01, 02)));

    }

}

public class GenericComparer<T> : IEqualityComparer<T>

    {

        private Func<T, T, bool> EqualsComparerDelegate { get; set; }

​

        private Func<T, int> GetHashDelegate{ get; set; }

​

        public GenericComparer(Func<T, T, bool> equalsComparer, Func<T, int> getHashDelegate) {

            this.EqualsComparerDelegate = equalsComparer;

            this.GetHashDelegate = getHashDelegate;

        }

​

        public bool Equals(T x, T y)

        {

            return this.EqualsComparerDelegate(x,y);

        }

​

        public int GetHashCode(T obj)

        {

            return  this.GetHashDelegate(obj);

        }

    }