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From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: Invoking parental methods (was: Java vs Ada 95)
Date: 1996/11/06
Message-ID: <EACHUS.96Nov6175318@spectre.mitre.org>#1/1
X-Deja-AN: 194991045
references: <E0ED6w.24D.0.-s@inmet.camb.inmet.com>
 <E0EIM2.A3p.0.-s@inmet.camb.inmet.com>
organization: The Mitre Corp., Bedford, MA.
newsgroups: comp.lang.ada
Date: 1996-11-06T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <1996Nov5.112527.1@eisner> kilgallen@eisner.decus.org (Larry Kilgallen) writes:

  > My problem, again, is maintainability in the face of genealogy shifts.
  > Since Ada 95 does not have a mechanism to do it with zero changes
  > to the body in the fashion of Macintosh Object Pascal, I am hoping
  > for 1.

   I really feel that a 'SUPER attribute would make the language more
useable, and maybe implementors will start providing it.  However,
until they do, we are stuck with the best solution being:

   For classes where you expect to need super, define:

   function Super(X: in Child) return Parent'Class;

   as a predefined operation.  Now (with my hand never leaving my
wrist), I can write Foobar(Super(Foob)); where it is not ambiguous,
and Foobar(Bar'(Super(Foob))); if I have to disambiguate.  The problem
is I'd like to find an efficient way to define the Super function so
that there are no accessability checks or the like and and you don't
have to override it all the time.  Any suggestions?  (Writing it the
other way round: function Super(X: in Child'Class) return Parent; has
the "advantage" that the override is forced, but the disadvantage that
you are much more likely to need a qualified expression.)



--

					Robert I. Eachus

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