From: "Mauricio Fernández" <batsman.geo@...>
Date: 2003-02-02T19:34:40+09:00
Subject: Re: no override

On Sun, Feb 02, 2003 at 06:41:45PM +0900, Mauricio Fern�ndez wrote:
> On Sun, Feb 02, 2003 at 04:51:08PM +0900, Tom Sawyer wrote:
> > is there any way to specifiy that a method can not be overrided? perfereably 
> > without throwing an error; rather if you try to override the method it simply 
> > dosen't happen.
> 
> Kind of evil, but works:
[...]

Forget that code, the following is much better as now:
 * you can use no_redef before defining methods in the base class, only
   derived classes are affected
 * you can "stack" the restrictions, ie if you have C < B < A, you can
   specify that some methods of A shouldn't be overloaded, and later
   that some in B shouldn't be either, and it'll just work.

And it gives a nice example of what class instance variables are good
for :-)

Drawback: method definition is somewhat slower, but _only_ definition.

batsman@tux-chan:/tmp$ expand -t 2 f.rb
module NoOverloading
  def no_redef(*args)
    @no_override ||= []
    args.each { |i| @no_override << i }
  end

  def __no_redef_list__
    supmethods = []
    (ancestors - [self]).each do |i|
      begin
        supmethods += ( i.__no_redef_list__ || [])
      rescue NameError
      end
    end
    (@no_override || []) + supmethods
  end

  def inherited sub
    class << sub
      def method_added(id)
        return if __no_redef_list__.index(id) == nil
        remove_method id
      end
    end
  end

end


class A
  extend NoOverloading
  no_redef :a, :b
  def a; puts "A#a"; end
  def b; puts "A#b"; end
  def c; puts "A#c"; end
  def d; puts "A#d"; end
end

class B < A
  def a; puts "B#a"; end
  def b; puts "B#b"; end
  def c; puts "B#c"; end
  def d; puts "B#d"; end
  no_redef :c
end

class C < B
  def a; puts "C#a"; end
  def b; puts "C#b"; end
  def c; puts "C#c"; end
  def d; puts "C#d"; end
end

c = C.new
c.a
c.b
c.c
c.d
batsman@tux-chan:/tmp$ ruby f.rb
A#a
A#b
B#c
C#d

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