From: Josh Cheek <josh.cheek@...>
Date: 2011-09-30T12:08:21+09:00
Subject: Re: Ruby mixin: extend or include?

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On Thu, Sep 29, 2011 at 9:48 PM, Jones Lee <joneslee85@gmail.com> wrote:

> I have following code:
>
> module CarHelper
>  def call_helpline
>    puts "Calling helpline..."
>  end
> end
>
> class Car
>  extend CarHelper
> end
>
> class Truck
>  class << self
>    include CarHelper
>  end
> end
>
> # Test code
> Car.call_helpline
> Truck.call_helpline
>
> In fact both 2 lines of test codes works. So is there any difference
> between the way I use 'extend' and 'include' (inside a singleton class
> of self)?
>
> --
> Posted via http://www.ruby-forum.com/.
>
>
The only difference that I know of is how the hooks get called:

module M
  def self.extended(obj)
    p "M is extended by #{obj.inspect} from line #{caller.first[/\d+/]}"
  end

  def self.included(klass)
    p "M is included in #{klass.inspect} from line #{caller.first[/\d+/]}"
  end
end

class C
  extend M
  class << self
    include M
  end
end

# >> "M is extended by C from line 12"
# >> "M is included in #<Class:C> from line 14"



As an aside, this is yet another argument against extending the object in
the included hook.

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