From: 7stud -- <bbxx789_05ss@...>
Date: 2008-03-26T15:22:50+09:00
Subject: Re: class_eval vs (class << object)

Ruby Freak wrote:
> What is the difference between class_eval and "class << object"?
> 
> It seems like they are the same. I am thinking that class_eval affects
> the greater class and "class_object" is used on a singleton class. Are
> they mutually exclusive?
> 
> Thanks

class Dog
  attr_accessor :age

  def initialize(a)
    @age = a
  end
end

Dog.class_eval{
  def show
    puts @age
  end
}


d1 = Dog.new(5)
d2 = Dog.new(2)

d1.show  #5
d2.show  #2


class Dog
  attr_accessor :age

  def initialize(a)
    @age = a
  end
end


d1 = Dog.new(5)

class << d1
  def show
    puts age
  end
end

d1.show  #5

d2 = Dog.new(2)
d2.show

--output:--
undefined method `show' for #<Dog:0x25260 @age=2> (NoMethodError)
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