dynamic instances extending mechanism for Metamorphosis

do.rb

require 'facets/kernel/constant'
require 'active_support/core_ext/module/attribute_accessors'

module Metamorphosis
  module Injector
    @@receiver = "Foo"
    
    def clutch cst_path, *directives, &blk
      raise ArgumentError unless cst = Object.constant([@@receiver, cst_path].join("::"))
      raise ArgumentError unless cst.is_a? Class or cst.is_a? Module
      
      # maybe that's not *that* safe, so I should see
      # what's possible with trace_var. Idée, aussi :
      # placer l'ensemble du code de slash dans un fiber
      # ou un thread quelconque, bref un truc qui
      # garantirait l'adressage. Mais je sais pas si ça
      # règle le problème des var. globales.
      $m = Module.new
      $m.module_eval(&blk)

      if directives.include? :instances
        # hophop les instances
        cst.extend(Module.new do
          def new *args, &block
            o = super
            o.extend($m)
            o
          end
        end)
      else
        cst.extend($m)
      end
    end
  end

  include Injector
end

module Foo
  class Bar
    def say what
      puts what
    end
  end
end

module Foo
  extend Metamorphosis

  #puts Bar.new.instance_eval("class << self; self; end").ancestors.inspect
  Bar.new.say "hello"
  puts

  clutch "Bar", :instances do
    puts "slashed! backward:"
    def say what
      super what.reverse
    end
  end
  
  #puts Bar.new.instance_eval("class << self; self; end").ancestors.inspect
  Bar.new.say "hello"
end