From: leon breedt <bitserf@...>
Date: 2005-06-25T20:33:55+09:00
Subject: Defining a method vs aliasing it

Hi,

I'm not exactly sure why defining a method with "def methodname"
versus aliasing it would behave differently.

My example code:


---< snip >---

module O1
  def self.append_features(base)
      super
      base.extend(ClassMethods)
      base.class_eval do
        class << self
          alias_method :inherited_without_o1, :inherited
          alias_method :inherited, :inherited_with_o1
        end
      end
      puts "Including O1 into #{base.inspect}"
  end
 
  module ClassMethods
    def inherited_with_o1(child)
      puts "O1: BEFORE WITHOUT"
      inherited_without_o1(child)
      puts "O1: AFTER WITHOUT"
      puts "O1: #{child.inspect}"
    end
  end
end
 
module O2
  def self.append_features(base)
      super
      puts "Including O2 into #{base.inspect}"
      base.class_eval do
        class << self
          alias_method :inherited_without_o2, :inherited
        end
      end
      base.extend(ClassMethods)
  end
 
  module ClassMethods
    def inherited(child)
      puts "O2: BEFORE WITHOUT"
      inherited_without_o2(child)
      puts "O2: AFTER WITHOUT"
      puts "O2: #{child.inspect}"
    end
  end
end
 
class Override
  include O1
  include O2
end
 
class Child1 < Override
end
 
class Child2 < Child1
end
 
class Child3 < Override
end


---< snip >---

This prints:


Including O1 into Override
Including O2 into Override
O1: BEFORE WITHOUT
O1: AFTER WITHOUT
O1: Child1
O1: BEFORE WITHOUT
O1: AFTER WITHOUT
O1: Child2
O1: BEFORE WITHOUT
O1: AFTER WITHOUT
O1: Child3


If I instead modify O2 to use the same approach as O1, I get the
expected output:


Including O1 into Override
Including O2 into Override
O2: BEFORE WITHOUT
O1: BEFORE WITHOUT
O1: AFTER WITHOUT
O1: Child1
O2: AFTER WITHOUT
O2: Child1
O2: BEFORE WITHOUT
O1: BEFORE WITHOUT
O1: AFTER WITHOUT
O1: Child2
O2: AFTER WITHOUT
O2: Child2
O2: BEFORE WITHOUT
O1: BEFORE WITHOUT
O1: AFTER WITHOUT
O1: Child3
O2: AFTER WITHOUT
O2: Child3



Why would using an alias to create the new "inherited" work, but a
"def inherited" not?


Help much appreciated..
Leon