Attempting to port groovy's delegate feature as an exercise

groovy-delegation.rb

# http://dontmindthelanguage.wordpress.com/2009/12/09/groovy-delegate-annotation/
# class Cleaner {
#    def doWork() { "clean" }
# }
# 
# class Employee {
#    def doWork() {  "work!" }
# }
# 
# class Manager {
#    @Delegate Employee employee = new Employee()
#    @Delegate Cleaner cleaner = new Cleaner()
# }
# 
# manager = new Manager()
# 
# assert "work!" == manager.doWork()

module GroovyDelegation
  def delegate(delegatee)
    @@_delegatees_ ||= begin
      class_eval do
        def method_missing(name, *args, &block)
          d = @@_delegatees_.find { |d| d.respond_to?(name) }
          d ? d.send(name, *args, &block) : super
        end
      end

      []
    end

    @@_delegatees_.push(delegatee)
  end

end
Object.extend GroovyDelegation

class Cleaner
  def work
    "clean"
  end

  def clean
    "clean"
  end
end

class Employee
  def work
    "work!"
  end
end

class Manager
  delegate Employee.new
  delegate Cleaner.new
end

require "test/unit"
class TestLibraryFileName < Test::Unit::TestCase
  def setup
    @manager = Manager.new
  end

  def test_groovy_style_delegation
    assert_equal "work!", @manager.work
    assert_equal "clean", @manager.clean
    assert_raise(NoMethodError) { @manager.nonexistent_method }
  end
end