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From: ncohen@watson.ibm.com (Norman H. Cohen)
Newsgroups: comp.lang.ada
Subject: Re: Ada.strings.bounded problems?
Date: 19 Jan 1995 21:59:29 GMT
Organization: IBM T.J. Watson Research Center
Distribution: world
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References: <TARJEIJ.95Jan11183331@ulrik.uio.no> <D29L78.J9@nntpa.cb.att.com>
 <3f3rl7$kts@watnews1.watson.ibm.com>
 <Mats.Weber-1301952029290001@mlma11.matrix.ch>
 <3fduto$ta7@watnews1.watson.ibm.com>
 <Mats.Weber-1701951908250001@mlma11.matrix.ch>
 <3fj8gs$h9b@watnews1.watson.ibm.com> <1995Jan19.124412@lglsun.epfl.ch>
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Date: 1995-01-19T21:59:29+00:00
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In article <1995Jan19.124412@lglsun.epfl.ch>, nebbe@lglsun.epfl.ch
(Robb Nebbe) writes: 

|> There couldn't have been any upward compatibility problems since you
|> couldn't override "=".

That's what Jean Ichbiah thought, but John Goodenough proved him wrong.

(A loophole resulted from the fact that you could override "=" for a
generic formal limited private type, but you could pass a nonlimited type
as the corresponding generic actual parameter.)

In any event, there is an upward compatibility problem with Ada-83
limited types: 

   package P is
      type T is limited private;
      function "=" (Left, Right: T) return Boolean;
      type R is
         record
            C: T;  -- makes R limited
            ...
         end record;
   private
      type T is ...;
   end P;

   package body P is
      -- Neither T nor R is limited here, so R has an "=" operator, but
      --    it uses predefined "=" for type T to compare Left.C and Right.C.
   end P;

--
Norman H. Cohen    ncohen@watson.ibm.com