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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: another way to shoot yourself in the foot?
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Date: Tue, 24 Jun 2008 22:50:10 +0200
Message-ID: <87abhablrx.fsf@ludovic-brenta.org>
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Date: 2008-06-24T22:50:10+02:00
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Robert A Duff writes:
> But in Ada 95, if you say:
> 
>     P(F(...));
> 
> where F returns limited, you are not passing a limited object,
> but an implicit reference to some object that already existed before the
> call to F.
[...]
> In Ada 2005, functions always return newly-created objects, which I
> think is appropriate.

This makes me wonder whether there is an actual difference in the way
the compiler handles such returns.  For example, has GNAT changed a
lot in this area?  Do the Ada 95 and Ada 2005 compatibility modes use
antirely different compilation strategies?

>     if F(...).Flag then ...
>
> The last one is pretty silly -- it creates a new limited object,
> grabs a boolean flag out of it, and then throws the whole thing
> away.

Yes but "grabbing a boolean flag" might consist in passing the limited
object as a parameter to a primitive function named Flag, which might
then pass it down to any number of subprograms with all sorts of side
effects.  One could write an arbitrarily large program like this :)

-- 
Ludovic Brenta.