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From: Per Sandberg <per.sandberg@bredband.net>
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Newsgroups: comp.lang.ada
Subject: Re: Enforcing initialization protocol for protected type
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NNTP-Posting-Date: Thu, 10 Sep 2009 17:47:29 UTC
Date: Thu, 10 Sep 2009 18:39:53 +0200
Xref: g2news2.google.com comp.lang.ada:8274
Date: 2009-09-10T18:39:53+02:00
List-Id: <comp.lang.ada>

The following will solve your problem but there is a catch.
The only compiler that will fix it is to my knowledge the most bleeding
edge gnat.
/Per

-----------------------------
       package p is
          type Protected_t;
          type initializer_t (Wrapped : not null access  Protected_t)
            is new ada.Finalization.Limited_Controlled with null record;

          procedure Initialize (self : in out initializer_t);
          procedure Finalize   (self : in out initializer_t);

          protected type Protected_t is
             entry tick;
             procedure Initialize;
             procedure finalize;
          private
             initializer : initializer_t (Protected_t'access);
          end;
       end p;

       package body p is
          protected body Protected_t is
             entry tick when True is begin
                null;
             end;
             procedure Initialize is
             begin
                null;
             end;
             procedure finalize is
             begin
                null;
             end;
          end;
          procedure Initialize (self : in out initializer_t) is
          begin
             self.Wrapped.Initialize;
          end;
          procedure Finalize   (self : in out initializer_t) is
          begin
             self.Wrapped.Initialize;
          end;
       end p;

Maciej Sobczak wrote:
> Consider the Needs_Constructor type from the code example in the Ada
> wikibook:
> 
> http://en.wikibooks.org/wiki/Ada_Programming/Types/limited#Initialisi...
> 
> Is it possible to ensure a given initialization protocol for protected
> types as well?
> 
> The problem is that protected types cannot have unknown discriminants.
> How can I ensure that objects of a given protected type are always
> initialized with a call to proper constructor function?
> 
> Note that wrapping a protected object in another one (presumably
> limited and private) would limit the possibility to perform timed
> entry calls on the target protected object and preserving this
> possibility is essential in my actual use case.
> 
> --
> Maciej Sobczak * www.msobczak.com * www.inspirel.com
> 
> Database Access Library for Ada: www.inspirel.com/soci-ada