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From: Michael Erdmann <michael.erdmann@snafu.de>
Newsgroups: comp.lang.ada
Subject: Usage of Interfaces with Ada 95
Date: Fri, 26 Sep 2003 18:36:31 +0200
Organization: http://www.snafu.de/~boavista
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Date: 2003-09-26T18:36:31+02:00
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Dear all,

i like to provide a package of elementary interfaces providing some 
basic concepts on which a application is build, for example a
so called Enumeration type

generic
   type Data_Type is private;

package Interface.Enumeration is

   type Object is abstract tagged null record;

   function HasMoreElements(
      This : in Object ) return Boolean is abstract;

   procedure Next(
      This   : in out Object;
      Result : out Data_Type) is abstract;

end Interface.Enumeration;

because Ada does not provide an elementary object as e.g. java
this package has to be provided as an generic making the use 
of the package a little bit complicated.

.....
  type Enumerator is private;
.....
  procedure Next(
     This   : in out Enumerator;
     Result : out  Data_Type );
.....

private
  package Reader is new Interface.Enumeration( Data_Type );

  type Enumerator is new Reader.Object with record
          Next : Element_Access := null;
       end record;


The whole thing becomes more and more complicated for other
concepts e.g. a Dictionary which involves two types.

I am realy wondering if there is a better (simpler) way of
providing such a concept library?


Regards
   M.Erdmann