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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Dispatching and Child Packages
Date: 21 Mar 2001 06:53:24 +0000
Organization: CodeFella
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Date: 2001-03-21T06:53:27+00:00
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"Klatt, Nathan" <nklatt@excite.com> writes:

> Is it possible to dispatch from within a child package?  The below code does
> not work.  If I collapse the child packages into their respective parents,
> it dispatches as expected.  (Ndk is an empty package.)

So why didn't you include it :-)

> ----------------------------------------------------------------------------
> package Ndk.Base is
> 
>     type Base is abstract tagged null record;
> 
> end Ndk.Base;
> ----------------------------------------------------------------------------
> package Ndk.Base.Child is
> 
>     procedure Do_Something (This : Base'Class);
>     procedure Real_Do_Something (This : Base) is abstract;
>
> end Ndk.Base.Child;
> ----------------------------------------------------------------------------
> package body Ndk.Base.Child is
> 
>     procedure Do_Something (This : Base'Class) is
>     begin
>         Real_Do_Something (This);
>     end Do_Something;

GNAT says:

ndk-base-child.adb:6:09: cannot call abstract subprogram "Real_Do_Something"
ndk-base-child.adb:6:28: class-wide argument not allowed here
ndk-base-child.adb:6:28: "Real_Do_Something" is not a primitive operation of "Base"

and the last remark is your problem. You need to declare
Real_Do_Something in Ndk.Base.

> package body Ndk.Sub.Child is
> 
>     procedure Real_Do_Something (This : Sub) is
>     begin
>         Ada.Text_Io.Put_Line ("Sub doing something...");
>     end Real_To_String;
               ^^^^^^^^^   ahem! I don't think you compiled this before
                           posting!

> end Ndk.Sub.Child;