Re: Legit Warnings or not

[Adam Beneschan <adam@irvine.com>]

On Jul 22, 3:16 am, Brian Drummond <br...@shapes.demon.co.uk> wrote:
> On Thu, 21 Jul 2011 14:54:35 -0700, Adam Beneschan wrote:
> > On Jul 21, 2:30 pm, Brian Drummond <br...@shapes.demon.co.uk> wrote:
>
> >> Seems that this implies that either (a: unlikely) the variable-sized
> >> component MUST remain in place in the record (which makes resizing it
> >> all but impossible) or (b: would work) the record must contain an
> >> ACCESS to it (in which case the implementation silently does something
> >> other than the declaration says).
>
> > (b) is pretty much how this would be implemented.  With regard to your
> > comment "the implementation silently does something other than the
> > declaration says":  the implication, [...] isn't warranted.  If there  
> > are no representation items, then a declaration says *nothing* about
> > how a type is represented.
>
> Thank you for the correction.
> ... the implementation silently does something other than I wrongly
> inferred from the declaration.
> I can live with that!
>
> I considered adding a comment that this would make representation clauses
> difficult, as you suggest.
>
> On the one hand, I would find it difficult to think of a practical use
> for a representation clause for this object ... on the other, unless
> aliasing this monster is specifically prohibited, there appears to be
> room for nasty corner cases. Is there such a rule?

Bob and I discussed this a little, above.  There's no rule against
aliasing the whole record, but that shouldn't pose a problem.  As for
aliasing just the dynamic array component, you can declare it
"aliased", but you can't do anything that would actually result in
aliasing (like use X.Name'Access) unless it is known that Name's size
can't change (which means that the compiler has to make sure the
pointer doesn't change either).  So I think the rules are sufficient
to avoid problems.

                                   -- Adam