From: Jim Freeze <jim@...>
Date: 2002-12-13T14:08:54+09:00
Subject: Re: Inheritance Question

Well duh, as soon as I hit send I realized that I had not looked far
enough and that what I had posted would not work. The way Matrix is
currently written, it is nearly impossible to extend through
inheritance. So, instead of using a 'is-a' type class, below is a
'has-a' type class. This method should work but has the drawback as
before, every public method of Matrix that you want exposed must be
wrapped.

require 'matrix'

class M 
  def initialize(a)
    @m = Matrix[*a]
  end
  private :initialize

  def self.[](*a)
    M.new(a)
  end
  def inv
    M[*@m.inv.to_a]
  end
  def inv!  # this is new. ie, not in Matrix
    @m = @m.inv
    self
  end

  def to_f
    M[*(@m.to_f.to_a)]
  end
  def to_f!  # this is new and handy!
    @m = @m.to_f
    self
  end
  def inspect; @m.inspect end
end

m = M[[1,2],[3,4]]
puts m.inspect
puts "m.class:            #{m.class}"
puts "m.to_f.class:       #{m.to_f.class}"
puts "m.to_f.inv.class:   #{m.to_f.inv.class}"
puts "m.inv.class:        #{m.inv.class}"
puts "m.to_f.inv.inspect: #{m.to_f.inv.inspect}"
m = m.to_f
puts "m.inv!.class:       #{m.inv!.class}"
puts m.inspect

---with output

Matrix[[1, 2], [3, 4]]
m.class:            M
m.to_f.class:       M
m.to_f.inv.class:   M
m.inv.class:        M
m.to_f.inv.inspect: Matrix[[-2.0, 1.0], [1.5, -0.5]]
m.inv!.class:       M
Matrix[[-2.0, 1.0], [1.5, -0.5]]


-- 
Jim Freeze
----------
Kin, n.:
	An affliction of the blood