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From: bobduff@world.std.com (Robert A Duff)
Subject: Re: Chunks of finalized
Date: 1997/10/04
Message-ID: <EHJ3F6.JA0@world.std.com>#1/1
X-Deja-AN: 277830941
References: <6129sn$n91$1@goanna.cs.rmit.edu.au> <3434F45A.37ED@gsfc.nasa.gov>
Organization: The World Public Access UNIX, Brookline, MA
Newsgroups: comp.lang.ada
Date: 1997-10-04T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <3434F45A.37ED@gsfc.nasa.gov>,
Stephen Leake  <Stephen.Leake@gsfc.nasa.gov> wrote:
>Do you want to call Finalize on the elements that have been Popped? =

That's presumably the issue.  These elements might be hanging on to some
expensive resource, and he wants to free that resource as soon as
possible -- not waiting for a whole chunk to be deallocated.

>... Another way is to assign another object to the
>stack slot, which will be done by the next Push.

Aha!  Thank you.

Why wait until the next Push (which might be a long time, or never)?
Inside the generic, you could declare:

    type Stack_Element_Holder(Present: Boolean := False) is
        record
            case Present is
                when False => null;
                when True => The_Element: Stack_Element_Type;
            end case;
        end record;

And then build the stack out of arrays of these things.  Then, whenever
you Pop, assign a "Stack_Element_Holder'(Present => False)" into the
vacated slot.  I think this achieves what the original poster wanted --
it will call Finalize on The_Element (if its controlled), and it will
also call Finalize on all controlled subcomponents of The_Element.  And
there's no need to pass in an extra finalization operation, nor to
handle subcomponents by hand.  It costs an extra Boolean component for
every stack element, though.

- Bob