phrogz_tweak.rb

# gem install remix
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 tweak_using(name,mod=nil)
		mod ||= Class.tweaks[name][self]
		include mod
	end
	def untweak(name,mod=nil)
		mod ||= Class.tweaks[name][self]
		uninclude mod
	end
end

module Kernel
	def apply_tweak(name)
		Class.tweaks[name].each{ |const,mod| const.tweak_using(name,mod) }
	end
	def remove_tweak(name)
		Class.tweaks[name].each{ |const,mod| const.untweak(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