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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Generic Library Units?
Date: Wed, 15 Oct 2014 09:21:06 +0200
Organization: cbb software GmbH
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Date: 2014-10-15T09:21:06+02:00
List-Id: <comp.lang.ada>

On Tue, 14 Oct 2014 21:29:16 -0300, hreba wrote:

> On 10/13/2014 04:45 AM, Dmitry A. Kazakov wrote:
>>
>> with Gui;
>> with GuiGtk.SimpleGad;
>> with Gui.SimpleGad;
>> package MainAux is
>>      package Toolkit is new GuiGtk;
>>      package SimpleGad is new Toolkit.SimpleGad;
>>      package GuiTK is new Gui (Toolkit, SimpleGad);
>> end MainAux;
>>
> Ok, did that too, and the error message disappeared.
> 
> Now in the package body of Gui.SimpleGad I have
> 
>     function Get (gad: BoolGadget) return boolean is
>     begin
>        return TKSG.GetBool (gad.widget.all);
>     end Get;
> 
> and get the error message
> 
> gui-simplegad.adb:78:39: expected type "GuiGtk.GadWidgets" defined at 
> guigtk.ads:38
> gui-simplegad.adb:78:39: found type "TK.GadWidgets" defined at 
> guigtk.ads:38, instance at gui.ads:10
> 
> So the compiler isn't aware that GuiGtk is the actual value to the 
> formal package TK. How do I tell him?

You can't. GuiGtk is a generic package. It cannot be actual of anything.
Actuals are *real* things. E.g. an instance of a generic package can be
actual of a formal package.

> ( The Gui package header is
> 
>     generic
>        with package TK is new GuiGtk(<>);	-- this is gui.ads:10
>        with package TKSG is new GuiGtk.SimpleGad;
>     package Gui is
>     ...
> )

Which has nothing to do with GuiGtk and GuiGtk.SimpleGad. Generic packages
know nothing about any instances of. That is the basic idea of being
"generic".

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de