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NNTP-Posting-Date: Fri, 11 Feb 2005 17:49:45 -0600
From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: setting 'Size and unchecked conversion safe here?
References: <mailman.131.1108161296.527.comp.lang.ada@ada-france.org>
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Date: Fri, 11 Feb 2005 17:49:45 -0600
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Date: 2005-02-11T17:49:45-06:00
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> What I'm not sure about is whether the unused 32
> bits are harmless or not (by definition). Thanks.
  An Unchecked_Conversion of dissimilar sizes is clearly unsafe, simply
because it's implementation defined how, or if, it works.
  But your problem appears to be the warning on
    for My_Access_To_Subprogram_Type'Size use 64;
ARM 13.3(42-43) recommends that a compiler should support this.
Presumably you don't care how the compiler places the 32 useful bits in
the 64 bit slot, so long as you get out what you put in.  So another
compiler might do it differently, but your program would still work
correctly.  So presumably the Gnat warning should be taken in the spirit
of "I notice you did this weird thing - are you sure you really meant to?"