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Newsgroups: comp.lang.ada
Date: Tue, 30 Jan 2018 15:32:53 -0800 (PST)
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Subject: Re: Iterable container as generic parameter
From: Lionel Draghi <lionel.draghi@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:50217
Date: 2018-01-30T15:32:53-08:00
List-Id: <comp.lang.ada>

As an overview :

   -- -------------------------------------------------------------------------
   --                             Cursors
   -- -------------------------------------------------------------------------
   generic
      type Container (<>) is limited private;
      type Cursor is private;
      with function First (Self : Container) return Cursor is <>;
      with function Has_Element (Pos : Cursor) return Boolean is <>;
      with function Next        (Pos : Cursor) return Cursor  is <>;
   package Cursors_Signature is end;

   -- -------------------------------------------------------------------------
   --                       The Image function
   -- -------------------------------------------------------------------------
   generic
      with package Cursors is new Cursors_Signature (<>);
      with function Image (C : Cursors.Cursor) return String is <>;
      with package Style is new List_Style (<>);
   function Image (Cont : in Cursors.Container) return String;

Image's formals reflect the three parameters of the function, no garbage, that's not to bad.

And instantiation is pretty easy :

      use Integer_Lists;
      package Integer_Lists_Cursors is new List_Image.Cursors_Signature 
        (Container => List,
         Cursor    => Cursor);
      
      function Image (C : Cursor) return String is
           (Integer'Image (Element (C)));

      function Integer_List_Image is new List_Image.Image
        (Cursors => Integer_Lists_Cursors,
         Style   => List_Image.Bracketed_List_Style);