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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: How to declare a generic formal type "covered" by another?
Date: Fri, 2 May 2014 17:33:45 +0200
Organization: cbb software GmbH
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Date: 2014-05-02T17:33:45+02:00
List-Id: <comp.lang.ada>

On Fri, 02 May 2014 08:12:01 -0700, Jeffrey Carter wrote:

> One can create a safe-pointer package that does not expose an access type (see 
> the PragmAda Reusable Components for an example), but the result tends to be 
> restricted to pointers to definite, non-limited types.

Safe-pointers do make much sense only with definite and non-limited types.

I pass the pointer type to the package of safe pointers. It also gives an
opportunity to have it pool-specific, when necessary. Yes, the object is
allocated on the client side, e.g.

   Handle.Set (new Object (...constraints...)); -- [*]

with Ada 2005 one could hide passed type returning anonymous access and
using limited return constructing function. Though, as experience shows, it
does not work well, especially the latter.

----
* This is a simplification, of course. If the object cannot be fully
initialized per Initialize. It looks like:

   declare
      Ptr : Object_Ptr := new Object (...);
      Thing : Object'Class renames Ptr.all;
   begin
      Handle.Set (Ptr);
      ... -- Initialize Thing
   end;

I wished Ada had a syntax to access allocated objects through class-wide
pointers. Something like:

   ... new X : Object (...) ...  do
       -- In this scope X refers to the allocated Object
   end new;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de