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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: This can't be done in Ada...or?
Date: 11 Feb 2005 18:52:24 -0500
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2005-02-11T18:52:24-05:00
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Ludovic Brenta <ludovic.brenta@insalien.org> writes:

> Robert A Duff writes:
> > The compiler can optimize away everything inside the "if
> > Logging_Enabled".  But it can't optimize away the evaluation of the
> > parameters unless it can prove the absence of side effects.  For
> > example:
> >
> >     Trace.Error(..., "Bad value of X " & Debug_Info(X));
> >
> > where Debug_Info is some user-defined function that produces useful
> > debug info about some complicated data structure called X.  It has
> > no side effects, but the compiler doesn't know that, usually.
> 
> What if Debug_Info is in a Pure package?  Does the compiler still have
> to consider possible side effects?

No.

It's usually a good idea to make things pragma-Pure when possible.
Unfortunately, it's not usually possible.  The restrictions on
pure packages are pretty severe.  No access types, for example.
And you usually need access types to make complicated data
structures.  I think Ada 2005 relaxes that restriction.

>...  I'm really curious.

- Bob