Re: Custom Storage Pool questions

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

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"J-P. Rosen" <rosen@adalog.fr> wrote in message 
news:shpg9b$t23$1@dont-email.me...
> Le 14/09/2021 à 08:23, Dmitry A. Kazakov a écrit :
>> Of course, a proper solution would be fixing Ada by adding another 
>> address attribute:
>>
>>  X'Object_Address
>>
>> returning the first address of the object as allocated.
> But you cannot assume that the object is allocated as one big chunk.
> Bounds can be allocated at a different place. What would be 
> X'Object_Address in that case?

The address of the real object, which is the bounds. (I'm using "object" in 
the Janus/Ada compiler sense and not in the Ada sense.) The only way I could 
make sense of the implementation requirements for Janus/Ada was to have 
every object be statically sized. If the Ada object is *not* statically 
sized, then the Janus/Ada object is a descriptor that provides access to 
that Ada object data.

Generally, one wants access to the statically sized object, as that provides 
access to everything else (there may be multiple levels if 
discriminant-dependent arrays are involved). That's not what 'Address is 
supposed to provide, so the address used internally to the compiler is the 
wrong answer in Ada terms, but it is the right answer for most uses (storage 
pools being an obvious example).

When one specifies 'Address in Janus/Ada, you are specifying the address of 
the statically allocated data. The rest of the object lives in some storage 
pool and it makes absolutely no sense to try to force that somewhere.

There's no sensible reason to expect 'Address to be 
implementation-independent; specifying the address of unconstrained arrays 
is nonsense unless you know that the same Ada compiler is creating the 
object you are accessing -- hardly a common case.

                                   Randy.