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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: GNAT GPL 2009 - issue with floating points?
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Date: Sun, 11 Oct 2009 12:27:15 +0200
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Date: 2009-10-11T12:27:15+02:00
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On Sun, 11 Oct 2009 11:33:04 +0200, Dirk Herrmann wrote:

> Dmitry A. Kazakov wrote:
>> On Sat, 10 Oct 2009 08:39:47 +0200, Damien Carbonne wrote:
>> 
>>> Thanks, now things are clearer. I understand that the compiler can not 
>>> determine Real'Size when it compiles the generic package, but when it is 
>>> instantiated, it should have then necessary knowledge.
>> 
>> Not if the generic body is shared, rather than expanded.
> 
> It seems that the rules for generics are designed to allow sharing.

They were.

Presently, I don't know if shared / contracted model is any alive.
Considering:

   generic
      type J is interface and I;
   package P is
      type T is new J with null record;
   end P;

When compiling P you cannot know if the actual for J does not have an
abstract operation which T does not implement.

Nevertheless one tries to pretend that generics still have some kind of
"contracts".

> It 
> surprises me, however, that there is no means to state that sharing is not 
> required, like, for example, a pragma or attribute. Such generics would offer 
> more implementation possibilities, since more information would be static.

In that case it should be a syntax element, not a pragma.

> I 
> understand the desire to support sharing, but for me it is a resource issue 
> (affecting ROM size and execution time) that might better be put under control 
> of the developer.

Then the solution is wrong. The desire is not to share bodies, but to have
contracts. With generics this goal is most likely unachievable.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de