Question

I’ve been having a look at explicit interface implementations in IL. The method Method in the following class (interface IA has a single Method() on it):

public class B : IA
    object IA.Method() {
        /* code */
    }
}

is compiled to the following IL method signature:

.method private hidebysig newslot virtual final instance object IA.Method() cil managed {
    .override IA::Method
    /* code */
}

My question is – why is the method name in IL IA.Method(), rather than just straight Method? What does this actually mean, and why doesn’t it work if it’s missed off? I can’t find anything in the ECMA spec or google about it.

Answer 1

This is because this way you can have a method multiple times.

public class B : IA
{
    object Method() {    }
    object IA.Method() {    }
}

The first is a normal method. The second is the interface implementation. Without the prefix you could not have both because you could not differentiate between them.

new B().Method(); // calls the normal method
((IA)new B()).Method(); // calls the IA interface method