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From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: Operation can be dispatching in only one type
Date: Thu, 19 Nov 2009 02:23:07 +0000 (UTC)
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Date: 2009-11-19T02:23:07+00:00
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> package Documents is
>
>     type Document is abstract tagged private;
>     type Text_Region is abstract tagged private;
>     type Marker is abstract tagged private;
>   ...
>     procedure Move_Text (Doc  : in out Document;
>                          From : in Text_Region;
>                          To   : in Marker)
>        is abstract;

  There's really no way at compile time to require a particular
relationship between two (or more) arbitrary parameters to a procedure.
If that's necessary, you usually combine them into a single object that's
a single parameter.  Thus if a Document could have up to 10 defined
Text_Regions and 20 Markers one could say

      type Document is abstract tagged private;
      -- Presumably includes an array or list of appropriate Text_Region
      -- descriptors and of Marker descriptors.

      type Text_Region_Ids is range 1 .. 10;
      type Marker_Ids is range 1 .. 20;

      procedure Move_Text (Doc  : in out Document;
                           From : in Text_Region_Ids;
                           To   : in Marker_Ids)
         is abstract;