Re: Polymorphism

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

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:5hbl45anxasb.1jn73i00zgy2i.dlg@40tude.net...
...
> I don't know why it is not allowed.

It *is* allowed. The problem in the OPs case is that the routine was 
abstract. Abstract routines must be overridden, but if it is private a 
client can't know that. Moreover, a client *cannot* override a private 
operation, so there could be no client in that case. Thus the original 
declaration is illegal.

As Simon pointed out, if the operation is concrete, it is fine to put it 
there. Then all clients that need to override it have to be child packages. 
Claw uses this extensively.

> Moreover, it probably would make sense
> to move all declarations of overriding into private

This is my coding standard. I only put new stuff into the visible part.

> or even further into the package body

That's not allowed as the tag has to be known when the type is frozen (that 
is, at the end of the specification). Of course, it would be possible to 
have a different set of rules where the tag isn't known at that point, but 
that's not the Ada design.

> because the fact of overriding is mere an implementation
> detail, since the primitive subroutine is there anyway no matter what.

Correct; that's why I put them into the private part.

                               Randy.