Re: Extending a type and Finalization

[Adam Beneschan <adam@irvine.com>]

On Jun 4, 1:06 pm, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
> On Thu, 4 Jun 2009 12:33:04 -0700 (PDT), Adam Beneschan wrote:
> > In addition to making an individual component a Limited_Controlled
> > type, you can use trickery using access discriminants to allow the
> > Initialize and Finalize routines to access the entire record.
> > Assuming P.T is limited, you can define something like:
>
> >    type Control_Type (Ref : access P.T'Class) is new
> >        Ada.Finalization.Limited_Controlled with null record;
>
> >    overriding procedure Initialize (Obj : in out Control_Type);
> >    overriding procedure Finalize   (Obj : in out Control_Type);
>
> > And then when defining TT:
>
> >    type TT is new P.T with record
> >       Control : Control_Type (TT'Access);
> >       ...
> >    end record;
>
> > Then when you declare an object of type TT, Initialize will be called
> > on the Control component, and the access discriminant Ref will give
> > you access to the entire record inside the Initialize and Finalize
> > routines.
>
> > (This idea isn't mine.  It might be Matthew Heaney's, but I'm not
> > sure.  The Control_Type declaration was adapted from a "shapes"
> > demonstration program, but I'm not sure where it came from.)
>
> I am not sure if this pattern is safe. What gives a guaranty that other
> components of TT are initialized before the Initialize gets called on
> Control and finalized after the Finalize gets called?

RM 7.6(12)

                            -- Adam