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From: matt@bacchus.esa.oz (Matt Atterbury)
Newsgroups: comp.lang.misc,comp.object,comp.lang.eiffel
Subject: Re: CHALLENGE: typing and reusability
Message-ID: <MATT.91Apr2093735@henry.bacchus.esa.oz>
Date: 1 Apr 91 23:37:35 GMT
References: <22032@yunexus.YorkU.CA>
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    <19MAR91.22493670@uc780.umd.edu>
    <18271:Mar2013:19:1091@kramden.acf.nyu.edu>
    <1991Mar20.214231.3411@neon.Stanford.EDU> <jls.669591628@rutabaga>
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In-reply-to: hoelzle@neon.Stanford.EDU's message of 31 Mar 91 21:57:21 GMT

In article <1991Mar31.215721.18687@neon.Stanford.EDU> hoelzle@neon.Stanford.EDU (Urs Hoelzle) writes:

   NOTE: ...

   Here's the scenario on which my claim is based:

   1) You haven't written A and B yourself but bought them from someone.
      That is, you cannot change A or B to inherit from a common base
      class.  I consider this as an absolutely unavoidable problem (more
      justification below).

      :
      :

How many of these problems would be solved if the language allowed the
addition of 'class utilities' (as described p.82 of Booch's OODwA) to
_any_ class at _any_ time (i.e. even if you don't have the source
code). I _believe_ you would still have to add such utilities to
sub-classes by hand due to Eiffel's default non-inheritance of
`methods' ? With this facility, you could make a bought-in class (BiC)
look exactly like you want it to.

You could do this now by subclassing the BiC and adding your utilities
to this new class, however the point of a HLL is to make the
programmer's life easier - consider buying an Eiffel encapsulation of
the entire X windows library and making all/many of its classes handle
the method jump_through_the_hoop !

[ a `class utility' is a non-primitive `method' which only uses
  primitive methods to do its work (i.e. doesn't play with state
  directly) ]

Note that I do not use Eiffel in Real Life so do not know for sure
that one can/cannot do the above. Also, I am probably commiting heresy
by not using the `right' terminology (e.g. method) :-).
--
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Matt Atterbury [matt@bacchus.esa.oz]      Expert Solutions Australia, Melbourne
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