Re: Record aggregates assignments and the black-box and else

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

Le Mon, 10 May 2010 17:20:08 +0200, Adam Beneschan <adam@irvine.com> a  
écrit:
> where R was previously uninitialized.  Even though R.A is supposed to
> have subtype "Natural", if it's uninitialized and thus garbage, it
> could have a negative value.  Thus, it's possible that this
> assignment, which is conceptually part of the assignment that creates
> the temporary object:
>
>    Temp_Object.A := R.A;
>
> could raise an exception if R.A happened to have a garbage negative
> value.
What should be involved here, is access to uninitialized value rather than  
range-check error. Unfortunately, I don't know a way to achieve this in  
Ada (except with some GNAT pragma which requires to initialize scalars so  
as to be sure it will later raise a range-check error if it was not  
properly initialized... still indirect)

> Anyway, assuming that the compiler determines that R.A will not raise
> an exception, and that B => 5 cannot raise an exception either, and
> there aren't any other reasons why R has to be preserved while the
> temporary object is being created, it might decide that there's no
> reason to create a temporary object.  This is permissible since the
> semantics would be exactly the same in all cases.  Then it's
> conceivable that the compiler could generate code that looks like
I agree with you about this semantic equivalence.


-- 
No-no, this isn't an oops ...or I hope (TM) - Don't blame me... I'm just  
not lucky