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From: "Martin Dowie" <martin.dowie@btopenworld.com>
Newsgroups: comp.lang.ada
Subject: Re: Is the Writing on the Wall for Ada?
Date: Thu, 18 Sep 2003 16:06:25 +0000 (UTC)
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Date: 2003-09-18T16:06:25+00:00
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"Mark A. Biggar" <mark@biggar.org> wrote in message
news:Iycab.95737$mp.45347@rwcrnsc51.ops.asp.att.net...
> You may or may not be able to turn this off.  The problem is that the
> Ada LRM says that on any assignment if an exception is raised when
> evaluating the RHS then the LHS shall be left unchanged.  So unless the
> compiler can determine that no such exception is possible it has to use
> a temporary.  This of course is yet another instance of solving the
> halting problem in the general case.

Sure, but for the "+ 1" it is simply a case of comparing the appropriate
'Last value for A - no need for a temporary here.


> Now. as Ada doesn't currently have ops like += they could be add to the
> language in such a way to not abide by the above rule.  But, that would
> break the semantic equavalence between "A := A + B;" and "A += B;".
> It also gets all messed up with issues involving user defined ops and
> controlled types.

That I don't like - actually I don't much care for these sorts of ops
anyway.