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Date: Fri, 07 Nov 2003 14:38:11 -0500
From: "Robert I. Eachus" <rieachus@comcast.net>
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Subject: Re: Clause "with and use"
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Date: 2003-11-07T14:38:11-05:00
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Martin Dowie wrote:

> I was also wondering how it would cope with non-limited types in
> situations like:
> 
>    A := A * B;
>    -- A and B are for the sake of arguement 'matrices', see the AI on
>    -- matrices & vectors ;-)
> 
> In this case could you safely manipulate A 'in-situ'?..

You see why ammending the reference manual is no easy task.  Of course 
we don't want to allow or require a compiler to mess up in that case, 
but want to permit it to do: A := B * C; right.  (That doesn't mean I 
can easily define what "right" means if A, B, and C are bit vectors.)

Oh, and just to rain a bit more on the parade, if A in your example is a 
3x4 matrix and B is 4x3, then is it legal to raise Constraint_Error 
before doing the arithmetic?  A more interesting question is that 
obviously if A in A := B * C; is indefinite, you want it to get the 
"right" constraint from the "*" function.  But what if the return value 
is declared indefinite?  Can it take its constraints from the target object?

-- 
                                           Robert I. Eachus

100% Ada, no bugs--the only way to create software.