Re: About 0Y interfaces

["Randy Brukardt" <randy@rrsoftware.com>]

"Pascal Obry" <pascal@obry.net> wrote in message
news:43552495.2050300@obry.net...
> Alex,
>
> > Firstly, interfaces are purely abstract, right? There's no way to
> > provide a default/partial implementation except creating an object type
> > which implements that interface.
>
> Right.

Correct. Interfaces are cheaper than full multiple inheritance, because
nothing concrete comes from them. You cna almost think of them as a
"property" of a tagged type -- it either has the interface (and thus
promises to have implementations of the primitive operations of the type) or
it doesn't.

> > Secondly, we can create an object type which implements two or more
> > interfaces.
>
> Right.
>
> > But I guess there's no multiple inheritance from classes, so
> > you couldn't use two implementations of two different interfaces
> > directly when creating a new type.
>
> There is no notion of interface implementation. Interfaces are inherited
> by a tagged object and implemented at this point.

You mean "tagged type". They also can be implemented by a task type or a
protected type. In all cases, the concrete operations either or are declared
at this point, or (in the case of a tagged type) are inherited from the
parent.

Personally, I find implementation inheritance to be more useful than
interface inheritance, but obviously others feel differently. And, in any
case, interfaces allow using OOP with tasks and protected types, which
wasn't a possibility in Ada 95.

                           Randy.