Re: AQ&S Guidance on pragma Elaborate_Body

["Nick Roberts" <Nick.Roberts@dial.pipex.com>]

Michael F Brenner <mfb@mbunix.mitre.org> wrote in article
<5jq9uc$kuf@top.mitre.org>...
> The link between pragma pure and thread safety is that thread safety is
> a memory concern, and the concept of a pure package is to be memory-free,
> and therefore as thread safe as any code can be. That is why optimizers
> are permitted to optimize away multiple calls to procedures in pure
> packages--they have NO memory. If they had memory, and therefore 
> potential thread-unsafeness, they ARE NOT pure, and it would be fibbing
> to mark them pure, and the optimized-away calls will be an undesireable
> effect on the execution of the code. The purity is transitive, since
> everything imported (withed) by a pure package must be pure. Therefore,
> if you call, for example, some pure_io.put_line several times during
> the debugging of a pure package, only the first pure_io.put_line would
> actually be called!
> 
> The second, and all further calls to pure_io.put_line would generate no
> code (i.e., in DEC Vaxen Ada language, would be optimized away).


Surely it would be a 'very poor' (substitute your favourite expletive)
compiler which 'optimized away' a second or subsequent call to a procedure
with only 'in' parameters defined in a pure package (as in Michael's
example)?

Moreover (and much earlier), if a compiler were to come across a procedure
which only has 'in' parameters declared in a pure package, surely to God it
should give a big fat warning message? I don't know if the language (Ada
95) allows it, but it would really be best for the compiler to give up
(with a fatal error), since this would certainly indicate a bug (wouldn't
it?).

Excellent post, by the way, Michael.

Nick.