Can I overload an == operator on an Interface?

Question

I have an interface like this:

public interface IFoo
{
  int A {get;}
  int B {get;}
}

and I have multiple classes implementing IFoo.
I

Answer 1

No, you can neither overload an operator on an interface, nor ensure that any implementors do so (as operator overloading is static in C# ).

Your best option is what you've done, to make IFoo inherit from IEquatable<IFoo> and use Equals(IFoo)

Answer 2

No, you can't. Overloading == requires static methods in one of the types you use, and an interface can't contain those. Extension methods can't help either. So on interfaces == is always using reference equality.

Note that a.Equals(b) will throw an exception if a==null.

Answer 3

What you're talking about here is an implementation detail, a Interface should not (cannot) define how it is implemented.

Answer 4

Besides CodeInChaos' answer you may be interested in reading Guidelines for Overriding Equals() and Operator ==.