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From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: Ada OO Mechanism
Date: 1999/06/03
Message-ID: <m36755mhm1.fsf@mheaney.ni.net>#1/1
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NNTP-Posting-Date: Thu, 03 Jun 1999 08:19:22 PDT
Newsgroups: comp.lang.ada
Date: 1999-06-03T00:00:00+00:00
List-Id: <comp.lang.ada>

Hyman Rosen <hymie@prolifics.com> writes:

> So you mean in Ada, I can write a dot(a,b) which will dispatch on
> either a or b?

Yes, if A and B have the same specific type. 

    <types AT and BT derive from T>

    A1, A2 : AT;
    B1, B2 : BT;

    AC1, AC2 : T'Class := <object has type AT>;
    BC1, BC2 : T'Class := <object has type BT>;

  begin
    
   .. := Dot (A, B);    -- illegal, detected at compile-time

         Dot (A1, A2);  -- legal
         Dot (B1, B2);  -- legal

         Dot (AC1, AC2);  -- legal, tags compared at run-time
         Dot (BC1, BC2);  -- legal, tags compared at run-time

         Dot (AC1, BC1);  -- legal, but run-time tag check fails,
                          -- and Constraint_Error is raised
  end;