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Date: Tue, 13 Sep 2005 21:23:22 +0200
From: Georg Bauhaus <bauhaus@futureapps.de>
Organization: future apps GmbH
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Newsgroups: comp.lang.ada
Subject: Re: generics in Ada 83
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Date: 2005-09-13T21:23:22+02:00
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REH wrote:
> Georg Bauhaus wrote:
> 
>>REH wrote:
>>
>>
>>>generic
>>>    type X is private;
>>>    with procedure Y(Z : in X);
>>>package Foo;
>>>
>>>I want to define a default for Y, but how can I without knowing X?
>>
>>Can you make generic stubs?
> 
> 
> Can you do that in '83?  I tried but I kept getting compiler errors.
> 

Something like this may work. Unless I misunderstand your problem, i.e..
The generic package Stubs.X_Operations provides default null procedures
for any private type X. You can use these operations as default
values when instantiating Foo.

generic
   type X is private;
   with procedure Y(Z : in X) is <>;
   -- lots of others
package Foo is end Foo;


with Stubs;
with Foo;

package Op_Maker is


   type Some_Type is record
      data: Natural;
   end record;

   type Some_Other_Type is record
      data: Character;
   end record;

   package Some_Operations is
      new Stubs.X_Operations(X => Some_Type);

   package Some_More_Operations is
      new Stubs.X_Operations(X => Some_Other_Type);

   use Some_Operations, Some_More_Operations;

   package A_Foo is new Foo(Some_Type);
   package Another_Foo is new Foo(Some_Other_Type);

end Op_Maker;

package Stubs is

   generic
      type X is private;
   package X_Operations is

      -- null procedures

      procedure Y(Z: in X);
      procedure Y2(U, V: in X);

   end X_Operations;

end Stubs;

package body Stubs is

   package body X_Operations is

      procedure Y(Z: in X) is
      begin null;
      end Y;

      procedure Y2(U, V: in X) is
      begin null;
      end Y2;

   end X_Operations;

end Stubs;