Interface "Implemented Member" Implementation should be smarter

[TonyValenti]

When implementing an interface, I should be able to return members that have a derived type of the specified type. IE:

public interface IInterface {
    IMember Member { get; }
}

public interface IMember {

}

public class Member : IMember {

}

public class MyClass : IInterface {

    //This does not work but should.  Generates CS0738. "Does not implmenent interface member..."
    //public Member Member { get; private set; } = new Member();

    //This does work.
    public IMember Member { get; private set; } = new Member();
}

In order to make the above work, I have to do something like this:

    public class MyClass : IInterface {
        public Member Member { get; private set; } = new Member();
        IMember IInterface.Member => this.Member;
    }

[DavidArno]

Why would you want to do this? I can't see any benefit at all to having the class provide a different implementation signature to the interface.

[jnm2]

Duplicate of #49, I believe.

[TonyValenti]

Because if you are working with an instance of my interface, I want to provide additional information that the interface itself might not expose. In order to make the above work, I have to do something like this and it isn't so tidy. It should just be automatic:

    public class MyClass : IInterface {
        public Member Member { get; private set; } = new Member();
        IMember IInterface.Member => this.Member;
    }

[Joe4evr]

I have to do something like this and it isn't so tidy.

The reason is that if you're accessing your instance as the interface, then you have absolutely no way to know that additional information exists outside of attempting to cast it.

[CyrusNajmabadi]

It should just be automatic:

Can you be more precise. What are the exact rules around which such members are generated? For example, say i have the following:

interface IFoo {
     int Foo { get; }
}

class C : IFoo {
    short Foo { get; }
}

Should that be allowed? What about user defined operators? etc. etc. In other words, what sorts of conversions should be allowed between the values in the bridge-member and the member the user created?