From: "David A. Black" <dblack@...>
Date: 2008-09-30T19:23:11+09:00
Subject: Re: extend keyword in class definition

Hi --

On Tue, 30 Sep 2008, ruud grosmann wrote:

>> It's neither. extend() is method that all objects have (classes are objects
>> too). It takes the methods from a module (in this case Forwardable) and adds
>> them as singleton methods to the object. Forwardable contains the method
>> 'def_delegators', which we see here has been added as a singleton method to
>> WriterDecorator.
>>
>
> thank you for your replies. But I'm afraid that I need some more
> explanation. Isn't a singleton method a method that applies to the
> singleton class of one object? And in this case we're talking about a
> class, not an object?
>
> As such, Forwardable is mixed in, is my first thought. What have I
> understood wrongly?

Classes *are* objects.

   c = Class.new        # c is an object whose class is Class
   c.extend(SomeModule)

Every class is an instance of the class Class, so you can extend
classes just like other objects.

I've always said that the answer to 75% of all questions about Ruby
is: Classes are objects :-) It's definitely a very key thing.


David

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