From: Michael Garriss <mgarriss@...>
Date: 2003-08-12T08:04:32+09:00
Subject: Re: newbie mixin questions

dblack@superlink.net wrote:

>Hi --
>
>On Tue, 12 Aug 2003, Michael Garriss wrote:
>
>  
>
>>Gennady wrote:
>>
>>    
>>
>>>----- Original Message -----
>>>From: "Michael Garriss" <mgarriss@earthlink.net>
>>>To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
>>>Sent: Monday, August 11, 2003 3:16 PM
>>>Subject: newbie mixin questions
>>>
>>>
>>>
>>>
>>>      
>>>
>>>>Hi,
>>>>   Just 2 questions:
>>>>
>>>>1) How can I mixin a class method (not an instance method)?
>>>>
>>>>
>>>>        
>>>>
>>>class A
>>> class << self
>>>   include SomeModule
>>>end
>>>end
>>>
>>>
>>>      
>>>
>>Very cool.  Will this require me to have two seperate modules though?
>>One for including class methods and the other of including the instance
>>methods.
>>    
>>
>
>No, modules are very modular and can fit almost anywhere :-)
>
>Here's a little illustration of how and why this works.
>
>Step 1: create a module
>
>  module SomeModule
>    def talk
>      puts "hi"
>    end
>  end
>
>and include it in a class in the usual way:
>
>  class A
>    include SomeModule
>  end
>
>Now all instances of A can talk:
>
>  A.new.talk         # hi
>
>Now, by way of parallel example: instead of class A, do the same thing
>with class Class:
>
>  class Class
>    include SomeModule
>  end
>
>Now all instances of Class can talk:
>
>  A.talk              # hi
>  String.talk         # hi
>  Class.new.talk      # hi
>
>That, by the way, is the heart of class methods: essentially, adding
>instance methods to objects which are instances of Class.
>
>The only problem is that you probably don't want all Class objects to
>talk; you only want A to talk.  So actually, instead of the above, you
>can do what Gennady did, which restricts the addition of 'talk' to
>just the one Class object (A):
>
>  class A
>    class << self         # operating just on A's singleton class,
>      include SomeModule  # so only A will gain the ability to talk
>    end
>  end
>
>  A.talk         # hi
>  String.talk    # error!  only added 'talk' capability to A
>
>
>David
>
>  
>
Thank you for the explanation.  I'm still a bit confused about something 
though:

module Example
    def method_I_want_to_be_a_class_method
       # whatever
    end
    def mehtod_I_want_to_be_an_instance_method
       # whatever
    end
end

class A
    include Example
    class << self
       include Example
    end
end

How do I seperate the class methods from the instance methods in the 
module?  In my above code I'll have one extra unwanted class and one 
extra unwanted instance method.

Michael