From: gwtmp01@...
Date: 2005-12-11T13:05:09+09:00
Subject: Re: About class methods


On Dec 10, 2005, at 8:34 PM, jonathan wrote:
> Hmm.  Ok, so there really is no singleton class for Myclass?  In other
> words, must the singleton always be associated with an instance and  
> not
> a class?

In Ruby, a class *is* an instance.  Specifically, a class is an instance
of the class Class.  So, yes, you can reference the singleton object
of a class:

	class <<Array
	end

More often it is done like this though:

	class Array
	  class <<self
	    # instance methods defined here will be
             # for the object Array (which happens to be a class)
	    # so these methods become 'class methods' for Array
	  end
	end

Alternatively you can do it like this:

	def Array.class_method1
	  # an instance specific method
	  # in this case the instance is the class object Array
	end

> Yea.  That is cool, but can you still do something like this:
>
> class Myclass
> end
>
> def extend_class( some_class )
>   code = %{ class #{some_class.class}_extension < #{some_class.class}
>               def new_method1
>               end
>               ...
>             end }
>   eval( code )
>
> extend_class( Myclass )
> x = Myclass_extension.new
> x.new_method1
> y = Myclass_extension.new
> y.new_method1

I'm not sure what you are getting at here.

Myclass.class is the particular object Class.  Because
all class objects are instances of Class.

	#{some_class.class}_extension

ends up being the string

	Class_extension

because Class.to_s is the string 'Class'.


If you want to subclass and add methods just do it:

class Myclass
end

class Subclass < Myclass
   def new_method1
   end
end

x = Subclass.new
y = Subclass.new
x.new_method1
y.new_method1