Re: Bounded String question

["Randy Brukardt" <randy@rrsoftware.com>]

"Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org> wrote in message 
news:nbl50v$8qq$1@dont-email.me...
> On 03/07/2016 04:16 PM, Randy Brukardt wrote:
>> "Xavier Petit" <xpetit@becoast.fr> wrote in message
>> news:56dc7e22$0$19749$426a34cc@news.free.fr...
>>
>> I don't know if this is relevant...
>>
>>> procedure Test_Bounded_String is
>>>    package Bounded_String is
>>>       type T (Max_Length : Natural := 100) is limited private;
>>
>> ...but a type like this can be completed with a non-limited type. That 
>> might
>> prevent the compiler from applying a limited-only optimization. (Another 
>> way
>> to say it is that this type is not inherently limited; non-limited views 
>> can
>> exist of such types, and a non-limited view would need an 
>> allocate-the-max
>> strategy [or a non-contiguous object].)
>
> The compiler knows the full type (which is limited) when it compiles the
> variable declaration and its associated elaboration code. Would it not be 
> able
> to use that information?

I'd be speculating to say anything about someone else's compiler. (One thing 
that we've all learned from the ARG is that what seems natural to one 
compiler implementer can require some amazingly twisted implementation in 
some other compiler. Best to never assume anything about some other 
compiler.)

But I will say that it would depend on how the compiler handles objects. For 
Janus/Ada, it is the type, not the object, that determines the memory 
management strategy, so we have to tie that down fairly early.

And, in any case, the presence of a partial view subtly changes the 
semantics of a type. (That's was added in Ada 2005 because the Ada 95 rule 
had the unpleasant effect of making the details of the full type relevant to 
the usage of the objects in some cases. It's rather a rather messy rule but 
it was added to preserve the notion that all you need to know about is the 
private type. (In Ada 95, you could get Constraint_Error when assigning two 
objects of a type with no visible discriminants. Yuck.) So those rules as 
well might cause a problem.

                                   Randy.