From: Pit Capitain <pit@...>
Date: 2006-06-25T20:40:40+09:00
Subject: Re: class << self?

Roger Johansson schrieb:
> ...
> what I dont get is why I only need to do the "class << self" thing when 
> aliasing static methods and not instance methods.

Roger, I think you haven't gotten an answer to this part of your 
question yet. I'm sure you wouldn't expect the alias keyword at the 
instance level in order to create an alias for an instance method:

   class C
     def m
       ...
     end
   end

   c = C.new
   c.alias :mnew :m  # create alias for the instance method C#m,
                     # but only for the instance c, or for all
                     # instances of C ???

So it makes sense to have the alias keyword where methods are normally 
defined: at the module/class level:

   class C
     def m
       ...
     end
   end

   class C
     alias :mnew :m  # create alias for the instance method C#m
   end

The same applies to singleton methods:

   o = Object.new

   class << o
     def m
       ...
     end
   end

   class << o
     alias :mnew :m  # create alias for the singleton method o.m
   end

The only difference to instance methods is that you can define singleton 
methods with an additional syntax:

   def o.m
     ...
   end

Now, what you call "static methods" are simply singleton methods of 
class objects, so again the same mechanisms apply:

   C = Class.new

   class << C
     def m
       ...
     end
   end

   class << C
     alias :mnew :m  # create alias for singleton method C.m
   end

I've used the same syntax as in the example above to show the similarity 
to other singleton methods. Normally you'd write this as:

   class C
     class << self
       def m
         ...
       end
     end
   end

   class C
     class << self
       alias :mnew :m  # create alias for singleton method C.m
     end
   end

or, for the definition part, as:

   class C
     def self.m
       ...
     end
   end

or even:

   def C.m
     ...
   end

As others have noted, just forget about "static methods". They don't 
exist in Ruby. There are only instance methods and singleton methods, 
nothing more.

Feel free to ask again if it's not clear.

Regards,
Pit