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From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: Freeing Pointers to classwide types
Date: 1998/10/09
Message-ID: <m3u31eupfd.fsf@mheaney.ni.net>#1/1
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NNTP-Posting-Date: Fri, 09 Oct 1998 08:03:14 PDT
Newsgroups: comp.lang.ada
Date: 1998-10-09T00:00:00+00:00
List-Id: <comp.lang.ada>

dennison@telepath.com writes:

> In article <m3emsix65f.fsf@mheaney.ni.net>,
>   Matthew Heaney <matthew_heaney@acm.org> wrote:
> 
> > I think the issue is, Should you use UD without also specifying a
> > storage pool too?  I would answer, No.  It has been my experience that
> > using the UD off-the-shelf is a recipe for disaster.
> >
> 
> Pardon my naivete', but how does a storage pool help the situation?
> Problems I know of that can happen with manual deallocation are not
> doing it when you should (leaks) and doing it too soon (dangling
> pointers).
> 
> I suppose it might help with the leak problem *if* the access type
> doesn't happen to be declared at the package level, but that seems to
> be pretty rare.  What good does it do in the more typical situation?

Sorry - I gave an imcomplete answer.  You also need to create a
controlled abstraction that does the allocation and deallocation.
Typically, the deallocation would be done automatically in the Finalize
operation.

The allocation is either done automatically during initialization, or is
a part of the work done by a constructor of some kind called by the
user.

Type Ada.Strings.Unbounded.Unbounded_String is a good example.  The
allocation is done when you call To_Unbounded_String, and the
deallocation is done when the scope ends in which the object is
declared.

In another post, I gave an example of automatical allocation during
Initialization.  (It was to allocate an active iterator whose type was
limited and unconstrained.)

The storage pool is necessary if you want to precisely control the time
and space behavior of allocation and deallocation.  But of course the
pool is hidden from the client of the (controlled) abstraction - the
access type, the storage pool, the call of new, and the call of
unchecked_deallocation, are all implementation details not available to
the client.