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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: What exactly is the licensing situation with GNAT?
Date: Mon, 17 Nov 2014 18:37:28 -0600
Organization: Jacob Sparre Andersen Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:23492
Date: 2014-11-17T18:37:28-06:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:dilqwcbqc502$.l6p0xx7myoiu.dlg@40tude.net...
> On Fri, 14 Nov 2014 16:24:14 -0600, Randy Brukardt wrote:
>
>> OTOH, I don't see why this would be any different than access types
>> vis-a-vis interfacing with C and the like. The type would have a
>> representation (likely one similar to access-to-subprogram), and that's 
>> the
>> problem for 'Unrestricted_Access - it needs a different representation to
>> support 'Unrestricted_Access from 'Access. And the representation needed 
>> for
>> 'Unrestricted_Access is incompatible with C (other than on GCC, which is
>> unusual). If you simply allowed any subprogram to match a subprogram 
>> type,
>> you couldn't allow interface to C. Or you'd have to have an accessibility
>> check on the use only for interface to C. Or some other messy rule - 
>> would
>> not gain anything.
>
> Except that whatever checks needed they will not include pointer checks. 
> If
> a nested subprogram cannot be passed to C, then it cannot. But the reason
> shall not be accessibility pointer check. The only reason allowed is
> "cannot implement pragma Convention".

Huh? The problem is that (some) nested subprograms cannot be passed to C. 
And allowing them to be passed in Ada is unconsonably expensive (at the very 
least, you'll need a mechanism to say that you don't want to pay for that 
overhead). What does pragma convention have to do with it?

                                      Randy.