From: Paul Brannan <pbrannan@...>
Date: 2003-12-17T00:10:13+09:00
Subject: Re: UnboundMethods Useless?

On Tue, Dec 16, 2003 at 05:09:00AM +0900, T. Onoma wrote:
> If I can only bind the method to an object of the same class from
> which I took it, then what's the point!? What am I missing?

It's not useless; I found at least one use for it in [ruby-talk:29122].

In trying to demonstrate an additional use, I came across this
peculiarity:

  class Base
    def foo
      puts "Base#foo"
    end
  end
  
  class Derived < Base
    def foo
      puts "Derived#foo"
      super
    end
  end
  
  base_foo    = Base.instance_method(:foo)
  Derived.__send__(:define_method, :foo, base_foo)
  
  # If I leave the following line out, then Derived.new.foo() results in:
  # test.rb:32: private method `foo' called for #<Derived:0x4027d0cc> (NameError)
  Derived.__send__(:public, :foo)
  
  # The following code produces (on Ruby 1.6):
  # test.rb:18:in `foo': bind argument must be an instance of Base (TypeError)
  #         from test.rb:18
  # But on Ruby 1.8 it prints Base#foo as expected.
  Derived.new.foo()

Can someone explain to me what's happening here? 

Paul