From: 7stud -- <bbxx789_05ss@...>
Date: 2011-08-23T11:37:03+09:00
Subject: Re: Gritty Details of super()

luke gruber wrote in post #1017907:
>
> Another, sort of related thing:
>
> Speaking of method lookup, class objects that have singleton classes
> embedded in singleton classes look up methods in the superclass's
> singleton class's singleton class (if it exists) and actually stop at
> the top-most singleton class of the original class object. A mouthful...
> I find this really cool if not pretty useless :)
>

I used that feature once in a solution I posted here.  :)
The op wanted to a method out of some other object's
lookup path, or some such thing.

> And like if a class
> object has 10 singleton classes with a greet() method defined in the
> seventh and eighth, and the subclass calls greet() in its sixth
> singleton class, it won't resolve.
>

Right.  A singleton class is just an object.  And all objects have a 
parent class and a singleton class.  But the singleton class of a 
singleton class is not in the first singleton class's lookup path.  Here 
is an example:

class Dog
  def Dog.greet
    puts 'hello'
  end
end

obj = Dog.singleton_class

obj.singleton_class.class_eval do
  def speak
    puts 'woof'
  end
end

Dog.greet
Dog.speak

--output:--
hello
ruby.rb:16:in `<main>': undefined method `speak' for Dog:Class 
(NoMethodError)


Or equivalently:

class Dog
  class << self
    def greet
      puts 'hello'
    end

    class << self
      def speak
        puts 'woof'
      end
    end

  end

end

Dog.greet
Dog.speak


--output:--
hello
ruby.rb:18:in `<main>': undefined method `speak' for Dog:Class 
(NoMethodError)

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