From: Sean O'Halpin <sean.ohalpin@...>
Date: 2011-02-18T02:49:31+09:00
Subject: Re: Defining class methods

On Wed, Feb 16, 2011 at 7:47 PM, Tony Arcieri <tony.arcieri@medioh.com> wrote:
> It seems there are 3 ways of defining class methods (at least in common
> usage):
>
> 1) Defining a method on self:
>
> def self.method
>
> 2) Opening up self and defining the methods directly:
>
> class << self
>  def method
>  ...
> end
>
> 3) Placing class methods into a module, and extending a class with that:
>
> module ClassMethods
>  def method
>  ...
> end
>
> extend ClassMethods
>
> --
>
> Which of these do you use and which do you prefer? Do you use all three? Do
> you think class << self is fugly and confusing?
>
> I used to use class << self quite frequently and have been shifting to using
> modules when dealing with a large number of class methods. I can't really
> say I'm a huge fan.
>
> --
> Tony Arcieri
> Medioh! Kudelski
>

It depends on whether and how you want to allow methods to be
overridden. Using #extend and 'def self.xxx' are not the same, viz:

    module A
      def run
        puts "A"
      end
    end

    class Foo
      extend A
    end

    class Bar
      extend A
    end

    Foo.run                         # => "A"
    Bar.run                         # => "A"

    module B
      def run
        puts "B"
      end
    end

    class Foo
      def self.run
        puts "foo"
      end
    end

    Foo.extend(B)
    Bar.extend(B)

    Foo.run                         # => "foo" - extend does not
override a def self.method
    Bar.run                         # => "B" - but it does override a
previously defined extension

    class Foo
      class << self
        def run
          puts "bar"
        end
      end
    end

    Foo.run                         # => "bar" - using 'class << self;
def method' ... same as 'def self.method'

Personally, I've come to prefer using #extend.

Regards,
Sean