method returning child, doesn't overrides declared method returning parent

[Jonathan M Davis]

On Tuesday, August 30, 2011 08:57:53 Mariusz Gliwiński wrote:
> I'm sorry - i provided wrong example. I had property in my code, and he
> didn't complained about getter, but setter (of course he can't diversify by
> different return values).
> 
> <code>
> interface Interface
> {
> 	void method(Interface);
> }
> class Class : Interface
> {
> 	void method(Class) {}
> }
> 
> void main() {}
> </code>
> 
> So, You're saying it should be possible, and this is DMD bug? So i'll report
> that.

This particular example is not a bug. A function which returns a Class can be 
used in exactly the same situations as one which returns an Interface, because 
an instance of Class _is_ an instance of Interface. However, an instance of 
Interface is not necessarily an instance of Class. So, if method takes an 
instance of Class, it can't take an instance of Interface unless it's also a 
Class. So, if you had

Interface i = funcWhichReturnsInterface();
Class c = new Class;
i.method(c); //This will compile.
c.method(i); //This won't compile.

it wouldn't work. Class' implementation of the method function must take 
_everything_ that Interface's method function can take, and it doesn't in your 
example.

- Jonathan M Davis