Re: Constraints in extended return

[Simon Wright <simon@pushface.org>]

Robert A Duff <bobduff@shell01.TheWorld.com> writes:

> Simon Wright <simon@pushface.org> writes:
>
>> This is all very well for providing a value where no constraint is
>> otherwise imposed, for example as an actual in a subprogram call, but
>> what about the case where there is a prior constraint?
>
> You get Constraint_Error if the constraint is wrong.
> But this isn't directly related to extended return statements.
> You get the same thing for old-fashioned returns:
>
>     function F(...) return String is
>     begin
>         ...
>         return "Hello";
>     end F;
>
>     X : String (1..100);
>
>     X := F(...); -- Constraint_Error
>
>> Is there any way for the extended return to determine the constraints of
>> the 'target'?
>
> No.  You can do that for 'out' parameters, but unfortunately not for
> function results.  So normally, you would avoid constraining at
> the call site, and do things like:
>
>    Output : constant Complex_Matrix := Transpose (Input);

Thanks, that's what I thought would be the case. This will constrain my
solution :-) but we all need boundaries!

> - Bob