Re: Question: inheritance from non-tagged types.

Re: Question: inheritance from non-tagged types.

[Samuel Tardieu]

>>>>> "Maxim" == Maxim Senin <maks@tech.swh.lv> writes:

Maxim> - is it correct to derive tagged type from non-tagged type like
Maxim>   here I derive Object from Controlled?

It is not correct to derive a tagged type from a non-tagged
type. However, Ada.Finalization.Controlled *is* a tagged type, so your 
question does not apply here, and your derivation is correct.

Maxim> - I derive Object from Controlled to allow garbage collection
Maxim>   for all Objects and their derivatives. Is it correct? Will it
Maxim>   work? I know garbage collection is not implemented in most
Maxim>   ADA compilers, but it's defined by language standard. I
Maxim>   believe that if I write program for "standard ADA compiler"
Maxim>   this code is correct. Is it true?

Having a type deriving from Controlled does not trigger any magic
garbage collection, it only lets you define Initialize, Adjust and
Finalize primitives that will be called respectively at initialization 
time, copy time and finalization time.

If an Ada[1] compiler uses a garbage collector, you don't need to use a
controlled object to trigger it, those are orthogonal issues.

However, if you want to write portable code, it is safer to use
instanciations of Ada.Unchecked_Deallocation to ensure that you will
reclaim unused storage[2].

  Sam

Footnotes: 
[1]  Yes, Ada, not ADA

[2]  Even if you have no guarantee that storage will get reclaimed in
     fact :)

-- 
Samuel Tardieu -- sam@ada.eu.org

Re: Question: inheritance from non-tagged types.

[Tom Moran]

>type Object is abstract tagged private;
>private
>        type    Object is new ADA.Finalization.Controlled with null record;
Do you really want this abstract, or not abstract?  It would help to
be consistent.