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From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: Eiffel and Java
Date: 1996/11/04
Message-ID: <EACHUS.96Nov4184435@spectre.mitre.org>#1/1
X-Deja-AN: 194640039
references: <55562c$nkd@mulga.cs.mu.OZ.AU>
 <1996Oct31.162218.8386@schbbs.mot.com>
organization: The Mitre Corp., Bedford, MA.
newsgroups: 
 comp.lang.eiffel,comp.lang.ada,comp.lang.sather,comp.lang.java.advocacy,comp.object
Date: 1996-11-04T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <JSA.96Nov2201641@alexandria> jsa@alexandria (Jon S Anthony) writes:

  > You mean something like, how does this work if you keep extending
  > the queues?  That should be OK.  If you mean something like, I
  > have a _different_ priority_queue thingy here (not derived from
  > queues) - will it just fit in and work?  No, that will require
  > going back and futzing...

   This looks like a case where you want interface inheritance, so
implement interface inheritance:

   generic
     type Stack_or_Queue is limited tagged private;
     type Element is tagged private;
     with function Pop(SQ: in Stack_or_Queue) return Element'Class is <>;
     with procedure Push(E: in Element; Onto: in out Stack_or_Queue) is <>;
     with function Is_Empty(SQ: in Stack_or_Queue) return Boolean is <>;
     -- etc.
   -- your procedure, function, or package goes here.

   For any Stack, Queue, Deque, etc., which matches the interface you
can instantiate your generic.  You can even figure out a meaningful
definition of Is_Empty for a queue connected to a pipe if that is what
you have.  (For example, delay until the other end of the pipe is
closed and return false, or until another element is put into the pipe
and return true.)


--

					Robert I. Eachus

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