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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
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Subject: Re: "Must instantiate controlled types at library level." Why?
Date: Thu, 13 May 2004 14:33:57 -0500
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Date: 2004-05-13T14:33:57-05:00
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"Peter C. Chapin" <pchapin@sover.net> wrote in message
news:Xns94E8433AB7894pchapinsovernet@207.106.93.237...
> Martin Krischik <krischik@users.sourceforge.net> wrote in
> news:2780491.NPbR8AFya6@linux1.krischik.com:
>
> > Well, here you have a good example of the difference of Ada and C++. Ada
> > has a complete ban on the construct while C++ goes out and about to ban
> > only the tricky part.
>
> It's interesting to reflect on these different approaches. C++ can get
> away with imposing such restrictions on nested functions because nested
> functions are rarely used in C++. In Ada similar restrictions on nested
> procedures would be entirely unacceptable. Consequently Ada imposes
> restrictions in a different place in order to avoid the same fundamental
> problem.

For what it's worth, the ARG is studying approaches to eliminate this
restriction. It would be replaced by a number of smaller ones (checks on
allocators, 'Access, return statements, and certain generic derivations).
The main reason is the inability to instantiate the containers packages in
nested scopes -- that seems like a nasty restriction.

                         Randy.