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NNTP-Posting-Date: Mon, 21 Mar 2005 16:37:32 -0600
From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: non-library level finalization
References: <VpOdnfiAMeCb36LfRVn-1Q@megapath.net>
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Date: Mon, 21 Mar 2005 16:37:32 -0600
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Xref: g2news1.google.com comp.lang.ada:9702
Date: 2005-03-21T16:37:32-06:00
List-Id: <comp.lang.ada>

>I forgot the obvious. The problem is not with a controlled *object*, but
>rather declaring a controlled *type*. So, you can do this by declaring a
>controlled type outside of the generic. Now, to make that useful, you'd have
>to figure out some way to figure out how to do the needed actions inside of
>the generic -- and *that* might prove difficult depending on what you need
>done. (For instance, registering a handler would work, but it too would have
>to be at library-level -- so you wouldn't have gained anything.)
  I considered the obvious
package Finalization_Helper is
  type Ptr_Type is access procedure;
  type Finalizer_Type is new Ada.Finalization.Limited_Controlled with record
    Last_Wishes_Ptr : Ptr_Type;
  end record;
  procedure Finalize(Finalizer : in out Finalizer_Type)  ...  is
  begin
    Finalizer.Last_Wishes_Ptr.all;
  exception
    when others=>null;
  end Finalize;

and then putting in the generic
  procedure Cleanup;
  Finalizer : Finalization_Helper.Finalizer_Type
    := (Last_Wishes_Ptr=>Cleanup'access);
but that has an access level problem.

>For a lot of generics, restricting to library level isn't a major concern
>(or, it's happened already, as is usually the case for tagged types). But
>your case may be different.
  It's merely unpleasing and maintenance error-prone to add an extra
package to instantiate the generic, and a Use clause to hide the fact of
the extra package.