Re: memory management in Ada: tedious without GC?

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> On Sun, 18 May 2008 20:50:48 -0700 (PDT), Matthew Heaney wrote:
>
>> On May 16, 4:42�pm, Maciej Sobczak <see.my.homep...@gmail.com> wrote:
>>>
>>> In Ada RAII is realized with controlled types. They are severely
>>> broken in that they are intrusive in the type hierarchy and they burn
>>> the whole budget for implementation inheritance,
>> 
>> No, this is wrong.  You can add in Controlled-ness as far down the
>> hierarchy as you like, by adding a controlled component.
>
> This is broken too:
>
> 1. You don't know exactly the order in which the Finalize of the controlled
> component gets called.  So if you access the container object over an
> access discriminant, that might be already invalid.

You know something about the order.  Initialize is bottom-up,
Finalize is top-down.  And when there are access discrims, the
order among subling-components is specified by the RM.

I would prefer a fully defined order, based on the declaration order.

> 2. Similarly, Initialize might be called before the container object is
> fully operational.

Same here.

> 3. Access discriminant would require controlled object to become limited,
> so must be the container.

Ada 2005 allows access discrims on nonlimited types.

> 4. The pattern is exposed to multiple inheritance diamond diagram problem,
> when such components are added independently.

I don't understand your point here.  Could you give an example of the
problem?

>> Furthermore, if you blow your budget in Ada, then you blow in C++ too,
>> since invoking Finalization in Ada is the same as invoking a dtor in C+
>
> Well, I suggest that the overhead required in C++ for maintenance virtual
> destructors should be lower than one Ada.Finalization. For example it does
> not require linked list of objects.

Ada's finalization does not require a linked list for stack-allocated
objects.  It does for heap-allocated ones.

> IMO, initialization/finalization hooks shall be definable for all types.

- Bob