From: Stu <stu@...>
Date: 2012-04-11T09:09:30+09:00
Subject: Re: A Beginner's Question about Metaprogramming

On Tue, Apr 10, 2012 at 6:33 PM, Phil Stone <lists@ruby-forum.com> wrote:

> I don't understand this code at all, especially the line "def
> self.metaclass; class << self; self; end; end". Where do all the names
> such as metaclass.instance_eval or class_eval come from? I'm really
> confused about this piece of code, and would appreciate some
> explanation. Sorry if these questions are rather basic.
>
> --
> Posted via http://www.ruby-forum.com/.
>


class << self is the same as def self.method

Look at a simpler example:

#Initial class definition:

class MyClass
  def hi
    "hi!!!"
  end
end

# Reopened with metaclass self.method style:

class MyClass
  def self.hello
    "hello"
  end
end


# Reopened with metaclass class << self style:

class MyClass
  class << self
    def goodbye
      "bye!!!"
    end
  end
end

> MyClass.new.hi
=> "hi!!!"
> MyClass.hello
=> "hello"
> MyClass.goodbye
=> "bye!!!"