Object oriented programming and interfaces

[Jesse Phillips]

On Monday, 4 December 2017 at 20:43:27 UTC, Dirk wrote:
> Hi!
>
> I defined an interface:
>
> interface Medoid {
>     float distance( Medoid other );
>     uint id() const @property;
> }
>
> and a class implementing that interface:
>
> class Item : Medoid {
>     float distance( Item i ) {...}
>     uint id() const @property {...}
> }
>
> The compiler says:
> Error: class Item interface function 'float distance(Medoid 
> other)' is not implemented
>
> Is there a way to implement the Item.distance() member function 
> taking any object whose class is Item?

I think everyone here has missed the reason.

The problem is that a derived type can do more, the interface 
only allows for two method calls while the class could 
theoretically do more.

If the compiler allowed the class it would let you access 
functions and members not available to the interfaces, and the 
function would still be passed a Medoid.

You could make a cast within your function, but then you're still 
really not handling the interface but that at least would be 
clear in the code rather than the compiler hiding it by ignoring 
the problem.