From: Robert Klemme <bob.news@...>
Date: 2003-05-13T16:30:17+09:00
Subject: State Pattern Implementation


Hi all,

I'd like to hear what people think: is this a reasonable implementation of
the state pattern?  (Apart from the fact, that class Foo is quite useless.
:-)  The other question is, whether rededinition of a method should issue
a warning in verbose mode (suppressed here by Kernel#no_warn()).

BOND$ cat state.rb

module Kernel
  def no_warn(&b)
    old = $-w
    begin
      $-w = false
      b.call
    ensure
      $-w = old
    end
  end
end

class Foo
  def initialize
    st1
  end

  def st1
    no_warn do
      def self.foo; 100; end
      def self.bar; 101; end
    end
  end

  def st2
    no_warn do
      def self.foo; 200; end
      def self.bar; 201; end
    end
  end
end

f = Foo.new

p f.foo
p f.bar

f.st1
p f.foo
p f.bar

f.st2
p f.foo
p f.bar
BOND$ ruby -w state.rb
100
101
100
101
200
201
BOND$

    robert