From: Yossef Mendelssohn <ymendel@...>
Date: 2008-10-08T03:48:27+09:00
Subject: Re: class << self

On Oct 7, 11:53 am, "Patrick Doyle" <wpds...@gmail.com> wrote:
> Would it be fair to say that 99% of the time there is no difference between
> the definitions of A#a, A#b, and A#c?
>
> class A
>   def self.a
>     puts "self.a"
>   end
>
>   def A.b
>     puts "A.b"
>    end
>
>   class << self
>     def c
>       puts "A.c"
>     end
>   end
> end
>
> It seems that the construct:
>
> class << self
>   def x
>   end
>
>   def y
>   end
>
>   def z
>   end
> end
>
> might be used primarily as a typing shortcut and that 99% of the time that's
> all it is.

Personally, I use class << self for several reasons:

- It reduces repetition
- I believe it's clear enough
- It makes searching for a method definition in your entire codebase
simpler
- It allows aliasing class methods
- It allows access control (public/private) of class methods

With that in mind, I see def self.meth as a shortcut for class << self
when all you're doing is defining a single method. If anything more is
to be done, it's cleaner overall to enter the eigenclass.

And I use self instead of the literal class name again to reduce
repetition. If you have

class A
  def A.a
    'got to .a'
  end
end

and you decide to change the class name from A to something else,
you're still defining A.a, which is now highly likely to be an error.
If you were using self.a or class << self, the method would still be
defined on whatever the class is now called.

--
-yossef