From: "Hal E. Fulton" <hal9000@...>
Date: 2001-05-11T11:06:17+09:00
Subject: [ruby-talk:14971] Module [instance] methods, append_features, etc.

Hello... I have a question. Actually, several.

When a module is mixed into a class via include, the
module instance methods become instance methods of
that class. So far, so good. (Listing 1 below.)

Q1. The module methods of that module do NOT become class
methods of the class. I'm not sure why that is.

Q2. I found the "append_features" trick to create a class
method using a module... but now the module instance
methods don't show up as instance methods of the class.
(Listing 2 below.) Why?

Q3. OK, maybe I don't "want" to bring in both class and instance
methods. Maybe I just "think I want it." I admit I don't have
an application in mind; I was just experimenting. Comments?

Q4. Why is it allowable to have a method definition within
the append_features body but not a second one? A second one
gives me a "nested method" error. I'm not understanding
something pretty basic.


Thanks,
Hal

# Listing 1

module MyMod

  def MyMod.aaa
    puts "aaa"
  end

  def bbb
    puts "bbb"
  end

end


class MyClass

  include MyMod

  def MyClass.ccc
    puts "ccc"
  end

  def ddd
    puts "ddd"
  end

end


x = MyClass.new

x.bbb           # bbb
x.class.ccc     # ccc
x.ddd           # ddd
x.class.aaa     # Undefined method



# Listing 2

module MyMod

  def MyMod.append_features(someClass)
    def someClass.aaa
      puts "aaa"
    end
  end

  def bbb
    puts "bbb"
  end

end


class MyClass

  include MyMod

  def MyClass.ccc
    puts "ccc"
  end

  def ddd
    puts "ddd"
  end

end


x = MyClass.new

x.class.ccc     # ccc
x.ddd           # ddd
x.class.aaa     # aaa
x.bbb           # Undefined method