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From: Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov>
Newsgroups: comp.lang.ada
Subject: Re: Generic default parameters
Date: 14 May 2002 10:02:20 -0400
Organization: NASA Goddard Space Flight Center (skates.gsfc.nasa.gov)
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Dmitry A. Kazakov <mailbox@dmitry-kazakov.de> writes:

> On 13 May 2002 12:42:45 -0400, Stephen Leake
> <stephen.a.leake.1@gsfc.nasa.gov> wrote:
>
> >Hmm, perhaps you _wanted_ IO.Handles.IO_Handle to be public, so
> >clients could do stuff. Simple :
> >
> >with Object.Handle;
> >package IO.Handles is
> >   type IO_Handle is private;
> >private
> >   package Handles is new Object.Handle (File_Descriptor, 
> >                                         File_Descriptor_Ptr);
> >   type IO_Handle is new Handles.Handle with null record;
> >
> >end IO.Handles;
> 
> Yes, but this would kill the nature of IO_Handle. It would be just a
> private or a tagged private type. All operations defined on Handle get
> invisible, as well as the fact that IO_Handle is a descendant of an
> instance of Object.Handle.

Well, I don't know what you want. You started out saying you wanted an
"incomplete" type in the public part, with a full type in the private
part that was from a generic instantiation. This gives you that.

If you want "all operations defined on IO_Handle" to be visible, then why
do you want an "incomplete" type in the public part?

Why should a client know that IO_Handle is a derived type, especially
since the parent type is invisible?

I guess I need to see an example of how you think a client would use
your new kind of type. That would make it clearer why a private type
won't work.

-- 
-- Stephe