From: Gennady <gfb@...>
Date: 2004-08-11T04:47:17+09:00
Subject: Re: Singleton class methods

David A. Black wrote:
> Hi --
> 
> On Wed, 11 Aug 2004, Gennady wrote:
> 
> 
>>Kyle Putnam wrote:
>>
>>>Hello,
>>>
>>>It seems these two syntaxes accomplish the same thing, or are there
>>>differences?
>>>
>>>    class Foo
>>>        class << self
>>>            def bar
>>>                # ...
>>>            end
>>>        end
>>>    end
>>>
>>>compared to...
>>>
>>>    class Foo
>>>        def Foo.bar
>>>            # ...
>>>        end
>>>    end
>>>
>>>Cheers,
>>>    Kyle
>>>
>>>
>>
>>Exactly the same from the functionality point of view (it differs in 
>>implementation, though). I personally prefer the first form, as when it 
>>comes to renaming a class, you can do it in one place. Also with this 
>>form you can do other nice things such as defining class attribute 
>>accessors with attr_reader, attr_writer or attr_accessor.
> 
> 
> One difference (I believe this was pointed out to me once by Guy
> Decoux, in response to the same question) is the scope of constants.
> If you open the new scope with << self, constants visible in method
> definitions will be those of that singleton class, rather than those
> of the original class.

That's kind of what I meant. It seems like when you do

class Foo
   def self.bar
   end
end

method "bar" is added to the list of methods of the original class Foo.

On the other hand, for

class Foo
   class << self
     def bar
     end
   end
end

a singleton class is created for class object "Foo" and method "bar" is 
defined in that singleton class, with all consequences. Hence, the 
difference in implementation.

It is how I see it. I may be completely wrong, though.

Gennady.

> 
> 
> David
>