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From: defaultuserbr@yahoo.com
Newsgroups: comp.lang.ada
Subject: Re: Some help for a C++ guy
Date: 8 Apr 2005 13:54:26 -0700
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defaultuserbr@yahoo.com wrote:
>
>    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;
>
>       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.

>>From research, looks like these subroutines that would be class methods
or whatever you want to call them must, in the words of on online
source:

"Non-virtual, non-const, non-static member functions map onto
subprograms, within the same package as the tagged type, whos first
parameter is of that tagged type or an access to the tagged type, or
who returns such a type."


That's a problem because that callback subroutine needs to be passed to
a function expecting some of the type BC_Completion_Handler_T, defined
as:

   type BC_Completion_Handler_T is access
      procedure (Status : in IO_Status_T);


Changing the that type would then break a bunch of other code.

I'm not sure I'm going to be able to find a solution, I'm afraid.


Brian