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List:       ruby-talk
Subject:    Re: Dynamically creating class methods
From:       "David A. Black" <dblack () rubypal ! com>
Date:       2009-06-30 21:42:43
Message-ID: alpine.LFD.2.00.0906301737060.14178 () rubypal ! com
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Hi --

On Wed, 1 Jul 2009, Shak Shak wrote:

> I want to create a class method which allows us to create further class
> methods, so something like:
>
> class Test
>  class << self
>    def create_method(name, proc)
>        self.class.send(:define_method, name, proc)
>    end
>  end
> end
>
> proc = lambda {puts 'Hello world'}
> Test.create_method(:foo, proc)
> Test.foo #want this
> Integer.foo #don't want this
>
> The problem with the above is that create_method adds foo to all
> classes. self.send on its own doesn't seem to do what I want - it adds
> foo as instance method instead.

There are three candidates for the class to which you might send the
:define_method message:

   1. Test
   2. Class
   3. the singleton class of Test

#3 is the one you want. The code you've written sends the message to
Class, and the self.send that you've tried sends it to Test.

Try this:

class Test
   def self.create_method(name, proc)
     s_class = class << self; self; end
     s_class.send(:define_method, name, proc)
   end
end

There are other ways (including using class_eval), but that's the
general idea.


David

-- 
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.rubypal.com
Now available: The Well-Grounded Rubyist (http://manning.com/black2)
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