using System;

using System.Collections.Generic;

​

public class Test: IEquatable<Test>

{

    public int SomeMutableValue;

    public bool Equals(Test other)

    {

        return other.SomeMutableValue == SomeMutableValue;

    }

}

​

public class Program

{

    public static void Main()

    {

        var dict = new Dictionary<Test, string>();

        var t1 = new Test(){SomeMutableValue = 1};

        Console.WriteLine(t1.GetHashCode());

        dict.Add(t1, "one");

        var t2 = new Test(){SomeMutableValue = 2};

        Console.WriteLine(t2.GetHashCode());

        dict.Add(t2, "two");

​

        var lookForMe = new Test(){SomeMutableValue = 2};

        Console.WriteLine(lookForMe.GetHashCode());

        Console.WriteLine(dict.ContainsKey(lookForMe)); //ops

    }

}