using System;

public class Program

{

    public static void Main()

    {

        var foo = new Foo();

        if(foo == null)

        {

        }

        if(null == foo)

        {

        }

​

    }

}

​

public class Foo

{

    public static bool operator ==(Foo a, Foo b)

    {

        Console.WriteLine("Foo operator == called");

        return ReferenceEquals(a, b);

    }

​

    public static bool operator !=(Foo a, Foo b)

    {

        Console.WriteLine("Foo operator != called");

        return !(a == b);

    }

​

    public override bool Equals(object obj)

    {

        Console.WriteLine("Foo Equals() called");

        return ReferenceEquals(this, obj);

    }

​

    public override int GetHashCode()

    {

        Console.WriteLine("Foo GetHashCode() called");

        return base.GetHashCode();

    }

}

​