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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Instantiating private types with discriminants?
Date: 11 May 2006 11:59:37 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2006-05-11T11:59:37-04:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

>...Both
> overloading and overriding are forms of polymorphism, so yes, in that sense
> it is similar. The difference becomes obvious if you have moved
> declarations of Type_A and Type_B into separate packages.

Right.  I suggest that "rick H" should rewrite his examples in the more
usual way -- one tagged type per package, and make them library
packages.

Then you can have a procedure that does dispatching calls to that
abstract subprogram, without having any visibility on the packages where
Type_A and Type_B are declared.

The abstract procedure is a place-holder -- the compiler needs to know
the parameter types and so forth.

> >         Iterator := Iterator.all.Next;
> 
> You don't need "all" here:
> 
>    Iterator := Iterator.Next;
> 
> Ada's pointers are transparent to record member/discriminant and array
> element (indexing) access.

Syntactically transparent, but not semantically.  If the ".all" syntax
weren't so darn ugly, I would recommend always using an explicit
dereference.  I believe there's an option in GNAT (a Restriction
pragma?) that allows you to force yourself to always say ".all",
which might not be a bad idea.

- Bob