Temporarily tweak classes to use new methods; idea (and necessary 'remix' functionality) stolen from banister(fiend)

phrogz_tweak.rb

# gem install remix; needed to uninclude modules
require 'remix'

class Class
  @tweaks = Hash.new{ |h,k| h[k]=Hash.new{ |h,k| h[k] = Module.new } }
  class << self; attr_reader :tweaks; end
  def when_tweaked_as(name,&block)
    Class.tweaks[name][self].class_eval(&block)
  end
  def apply_tweak(name,mod=nil)
    mod ||= Class.tweaks[name][self]
    include mod
  end
  def remove_tweak(name,mod=nil)
    mod ||= Class.tweaks[name][self]
    uninclude mod # needs 'remix' gem
  end
end

module Kernel
  def apply_tweak(name)
    Class.tweaks[name].each{ |const,mod| const.apply_tweak(name,mod) }
  end
  def remove_tweak(name)
    Class.tweaks[name].each{ |const,mod| const.remove_tweak(name,mod) }
  end
  def using_tweak(name)
    begin
      apply_tweak(name)
      yield
    ensure
      remove_tweak(name)
    end
  end
end

if __FILE__==$0 then
  class String
    when_tweaked_as(:swizzlers) do
      def swizzle; reverse; end
    end
    when_tweaked_as(:gerdunken) do
      def thunk; raise "NO THUNKING"; end
    end
  end

  class Integer
    when_tweaked_as(:swizzlers) do
      def swizzle; to_s.reverse.to_i; end
    end
  end

  p "foo".swizzle rescue p "NO String#swizzle  before"
  p "foo".thunk   rescue p "NO String#thunk    before"
  p 24.swizzle    rescue p "NO Integer#swizzle before"
  using_tweak :swizzlers do
    p "foo".swizzle rescue p "NO String#swizzle  during"
    p "foo".thunk   rescue p "NO String#thunk    during"
    p 24.swizzle    rescue p "NO Integer#swizzle during"
  end
  p "foo".swizzle rescue p "NO String#swizzle  after"
  p "foo".thunk   rescue p "NO String#thunk    before"
  p 24.swizzle    rescue p "NO Integer#swizzle after"

  #=> "NO String#swizzle  before"
  #=> "NO String#thunk    before"
  #=> "NO Integer#swizzle before"
  #=> "oof"
  #=> "NO String#thunk    during"
  #=> 42
  #=> "NO String#swizzle  after"
  #=> "NO String#thunk    before"
  #=> "NO Integer#swizzle after"
end

very cool, nice work, though i find the when_tweaked_as syntax inside Integer and so on a tiny bit jarring, but it's perhaps because im not used to it yet. I am currently aiming for the current syntax:

tweak :MyTweaks do
  class String
    def hello; :hello; end
  end

  class Fixnum
    def bye; :bye; end
  end
end

using :MyTweaks do
  "john".hello #=> :hello
  5.bye #=> :bye
end

Cheers :)