From: ahoward <ahoward@...>
Date: 2002-12-14T02:51:03+09:00
Subject: Re: Inheritance Question

On Sat, 14 Dec 2002, ts wrote:

G> >>>>> "a" == ahoward  <ahoward@fsl.noaa.gov> writes:
G>
G>
G> a> for instance, if all calls to Matrix.method made from inside Matrix instance
G> a> methods are replaced with type.method - Matrix works identically and becomes
G> a> inheritable.
G>
G>  Matrix is inheritable : the problem is with delegation


  require 'matrix'

  #the problem
  class MyMatrix < Matrix
  end

  mm = MyMatrix[ [42] ]
  p mm.type		  # >> MyMatrix
  p mm.to_f.type	  # >> Matrix


  #the fix
  class Matrix
    def collect
      rows = @rows.collect{|row| row.collect{|e| yield e}}
      #Matrix.rows(rows, false)
      type.rows(rows, false)
    end
  end

  mm = MyMatrix[ [42] ]
  p mm.type		  # >> MyMatrix
  p mm.to_f.type	  # >> MyMatrix



i thinks it's a problem when you inherit from a class and cannot re-use the
instance methods when they 'jump' outside the inherited class...  eg.  the
only way around this is to completely rewrite evey Matrix instance method
which refers to a Matrix class method.  technically this IS inheritable but
it's a bitter pill to swallow...

-a


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