From: "David A. Black" <dblack@...>
Date: 2009-07-22T06:20:33+09:00
Subject: Re: define_method in inheritance

Hi --

On Wed, 22 Jul 2009, Juston Davies wrote:

> I had a quick question about something I had read in a book "The Ruby
> Way." The author talks about different ways to dynamically define
> methods during runtime using something similar to the snippet below.
>
>  def define_method (name, &array)
>    self.class.send(:define_method, name,&array)
>  end
>
> This opens up the scope of a given class so any other class could add
> methods on the fly. My question is that if I were to insert this code
> into a parent and then invoke it on a child would the new method be
> defined within the scope of the child or the parent? I'm concerned
> that this might result in adding methods into all the children rather
> than just the desired one. Let me know what you think. Thanks in
> advance!

It will define the method in self.class, which will be the class of
whatever object you call it on. The new method will also be available
to instances of subclasses of that class.

class A
   def define_method(name, &block)
     self.class.send(:define_method, name, &block)
   end
end

class B < A
end

class C < B
end

b = B.new
b.define_method(:x) { puts "In x!" }

b.x       # In x!

c = C.new
c.x       # In x!

a = A.new
a.x       # Unknown method x


David

-- 
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