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From: hreba <hreba@terra.com.br>
Newsgroups: comp.lang.ada
Subject: Generic Library Units?
Date: Sun, 12 Oct 2014 11:38:16 -0300
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Date: 2014-10-12T11:38:16-03:00
List-Id: <comp.lang.ada>

Hi,

I am writing a facility for graphical toolkits named Gui as a generic 
package and GuiGtk as an actual parameter package. As Gui grew I 
splitted it up into Gui and Gui.SimpleGad. More by trial and error than 
by strict reasoning (and with the help of John Barnes' book) I ended up 
with the following package structure:

gui.ads: parent generic package
-------
with GuiGtk;
generic
    with package TK is new GuiGk(<>);
package Gui is
    ...
end Gui;

gui-simplegad.ads: child package for Gui
-----------------
generic
package Gui.SimpleGad is
    ...
end Gui.SimpleGad

guigtk.ads: actual parameter package for Gui
----------
generic
package GuiGtk is
    ...
end GuiGtk;

mainaux.ads: auxiliary package for the main program
-----------
with Gui;
with GuiGtk;
with Gui.SimpleGad;
package MainAux is
    package Toolkit is new GuiGtk;
    package GuiTK is new Gui(Toolkit);
    ...
end MainAux;

test.adb: Main program
----
with MainAux;
procedure Test is
    ...
end Test;

Now my questions are:

1. Is this really the shortest form? (Why can't I contract the 2 lines 
under "package MainAux is" into "package GuiTK is new Gui(GuiTK)"?

2. The generic package file has to depend on a specific actual package?
If one day I decide to use, let's say Qt, then I will have to change the 
respective lines in gui.ads into
    package Toolkit is new GuiQt; ?

3. My actual package GuiGtk has grown considerably, so I want to split 
up that too into parent and child package, adding something like

guigtk-simplegad.ads:
----------------
package GuiGtk.SimpleGad is
   ...
end GuiGtk.SimpleGad;

No attempt to initialize this in MainAux or call it in Test has been 
working so far. Can somebody please give me a hint?
-- 
Frank Hrebabetzky		+55 / 48 / 3235 1106
Florianopolis, Brazil