Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!gatech!bloom-beacon!clyde!concour!marcap
From: marcap@concour.CS.Concordia.CA (Marc Pawlowsky)
Newsgroups: comp.lang.eiffel
Subject: redefining constant features
Summary: Error on Pass 2
Message-ID: <976@clyde.Concordia.CA>
Date: 12 Jul 89 16:38:04 GMT
Sender: news@Clyde.Concordia.CA
Reply-To: marcap@concour.CS.Concordia.CA (Marc Pawlowsky)
Organization: Concordia University, Montreal Quebec
Lines: 42

Why is it not legal to redfine a constant feature??

My problem:

  Class image export nb_directions ....

    feature
      nb_directions:INTEGER is 4;

  Class hex_image export nb_directions ...
    inherit image redefine nb_directions ....

    feature
      nb_directions:INTEGER is 6;

 is an error on Pass 2 
    Constant feature may not be redefined: nb_directions

yet if I change the code so that in image

  nb_directions:INTEGER is
    do Result := 4 end;

and in hex_image

  nb_directions:INTEGER is
    do Result := 6 end;

the program compiles.

**************************************************************************
Why I believe this is wrong.
*************************************************************************

1.  Using information sharing it is no buisness of the ancestors how a 
    value is calculated.  So there is a consistency problem.

2.  There is no reason why the redefinition should not be allowed.  At all
    times the constant value can have only one possibility.  Is the trouble
    that a procedure in the parents class might not work if a child calls
    it with a constant redefined.  If so that is a case where the child
    whould redefine the routine.