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Subject: Re: Some help for a C++ guy
Date: 8 Apr 2005 10:49:17 -0700
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Date: 2005-04-08T10:49:17-07:00
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Simon Wright wrote:


> It sounds from your original question as though you want to use
tagged
> types, roughly the equivalent of classes & inheritance in C++.

Here's my current attempt:

with MIL_STD_1553;
with OS_Types;

package Message_Handler is

   package M1553 renames MIL_STD_1553;

   type Handler is
      tagged record
         Data_Buf_Ptr   :  M1553.Data_Buf_VPtr_T := new M1553.Data_Buf;
         Stat_Buf_Ptr   :  M1553.Status_Buf_VPtr_T :=
           new M1553.Status_Buf_T;
      end record;


      -- the following are the primitive operations of the type
      procedure Message_Callback (Status : in M1553.IO_Status_T);

      function Num_Message_Callbacks return OS_Types.Unsigned_Word;

      function Num_Errors return OS_Types.Unsigned_Word;


end Message_Handler;

That compiles OK. In the client test package, I have:

with Message_Handler;

pragma Elaborate_All(Message_Handler);

   Handlers : Array (0..1) of Message_Handler.Handler;

That's all good too.

However, the first place that uses something from Message_Handler:

      Callbacks := Handlers(0).Num_Message_Callbacks;

Fails to compile, with an error message:

no selector "Num_Message_Callbacks" for type Handler defined at
message_handler.ads


So obviously I'm either defining things wrong or using what I have
defined incorrectly.



Brian