From: 7stud -- <bbxx789_05ss@...>
Date: 2011-03-26T08:43:48+09:00
Subject: Re: How to get the value of a singleton class?

Joey Zhou wrote in post #989179:
> Here is a sample code:
>
> str = "ABC"
> class << str
>   p self
> end
>
> What I get is somthing like "#<Class:#<String:0x15d4bb0>>".
>
> If "p str", there's an error message:
>
> x.rb:3:in `singletonclass': undefined local variable or method `str' for
> #<Class:#<String:0x1625bf8>> (NameError)
>
> How can I get the value of str("ABC") within the class << str;...;end
> block?
>

By creating a method that does just that:

str = "ABC"

class << str
  def show
    puts self
  end
end


str.show

Because str calls the show() method, inside show() self is equal to str.

You have to realize that when you write this:

> str = "ABC"
>
> class << str
>   p self
> end
>

it's is the same as doing this:


class MyClass
  p self
end

obj = MyClass.new

p obj

--output:--
MyClass
#<MyClass:0x401bfbf8>


...and wondering why 'p self' and 'p obj' don't produce the same 
results.  Inside a class, but outside of any method definitions, self is 
equal to the class--that's why 'p self' gives you the class name.

When you do this:

class << str
  ..
  ...
end

you have opened up a class--what's called the 'eigenclass' of str. 
Therefore, everywhere inside there, but outside any method definitions 
self is the class, and will never be equal to str.

-- 
Posted via http://www.ruby-forum.com/.