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NNTP-Posting-Date: Fri, 08 Apr 2005 19:19:01 -0500
From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: Some help for a C++ guy
References: <1113001402.404239.275940@z14g2000cwz.googlegroups.com>
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Date: Fri, 08 Apr 2005 19:19:02 -0500
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Xref: g2news1.google.com comp.lang.ada:10358
Date: 2005-04-08T19:19:02-05:00
List-Id: <comp.lang.ada>

Why not save pointers to the Handler objects instead of the procedures?

You have something like:

1) type BC_Completion_Handler_T is access
     procedure (Status : in IO_Status_T);
   ...
2) -- in the routine that does callbacks you have:
   Saved_Completion_Handler_Ptr : BC_Completion_Handler_T;
   procedure Register_Message_Callback (msg_id : ... ;
                           Callback_Ptr : BC_Completion_Handler_T) is
   begin
     Saved_Completion_Handler_Ptr := Callback_Ptr;
   end Register_Message_Callback;

3) -- and then in various places therein you have the actual callbacks
   Saved_Completion_Handler_Ptr.all (Status);


change the above to something like:

1) type BC_Completion_Handler_T is access all Handler;
   ...
2) -- then in the routine that does callbacks you have:
   Saved_Completion_Handler_Ptr : BC_Completion_Handler_T;
   procedure Register_Message_Callback (msg_id : ... ;
                           Callback_Ptr : BC_Completion_Handler_T) is
   begin
     Saved_Completion_Handler_Ptr := Callback_Ptr;
   end Register_Message_Callback;

3) -- and then in various places therein you have the actual callbacks
   Completion_Handler (Saved_Completion_Handler_Ptr, Status);


that would require a single point change to (1), and a global replace
   Saved_Completion_Handler_Ptr.all (Status);
   =>
   Completion_Handler (Saved_Message_Ptr, Status);
Registration of an array of Handler could then be done in a loop.

Of course you would also do global replacements
BC_Completion_Handler_T   =>  BC_Message_T
Saved_Completion_Handler  =>  Saved_Message
Callback                  =>  To_Callback
so as not to confuse readers, leading to:

1) type BC_Message_T is access all Handler;
   ...
2) -- then in the routine that does callbacks you have:
   Saved_Message_Ptr : BC_Message_T;
   procedure Register_Message_To_Callback (msg_id : ... ;
                           To_Callback_Ptr : BC_Message_T) is
   begin
     Saved_Message_Ptr := To_Callback_Ptr;
   end Register_Message_To_Callback;

3) -- and then in various places therein you have the actual callbacks
   Completion_Handler (Saved_Message_Ptr, Status);