From: Bob Calco <robert.calco@...>
Date: 2002-06-22T04:11:23+09:00
Subject: RE: Mixin using append_features and class<<self do not work together

Philip:

Here something conceptually related to what you are trying to do. This is a
teaser from Chapter 6 of the book Rich Kilmer, Dana Moore and I are writing,
namely, the _Ruby Developer's Handbook_, for Sams (to be published in early
2003). The chapter covers Ruby's idiomatic support for meta-programming in
considerable depth.

-------------------

module Adaptable
  def add_method( scope, name, args, code )
    instance_eval <<-END
      class << self
        #{scope}
        def #{name} ( #{args} )
          begin
            #{code}
          rescue => err
            puts err
          end
        end
      end
    END
  end
  def remove_method( name )
    instance_eval "undef #{name}"
  end
end

o = Object.new

class << o
  include Adaptable  # add Adaptable to this instance of the Object class
end

o.add_method :public, :fact, :n, <<-END
  if n == 0 then
    1
  else
    n * fact( n-1 )
  end
END

o.fact( 5 )  #=> 120

o.remove_method :fact

o.fact( 5 )  #=> (NoMethodError)


-------------------------------------

This should anwer some of your questions, and open you eyes to more than a
few possibilities.

Enjoy!

-- Bob Calco


-----Original Message-----
From: Philipp Meier [mailto:meier@meisterbohne.de]
Sent: Friday, June 21, 2002 2:35 PM
To: ruby-talk ML
Subject: Mixin using append_features and class<<self do not work
together


Hello to all,

First, I'm new to ruby so please forgive if I read over the solution in
the ruby doc or pickaxe book.
I'd like to know if it's possible to add a method to an object
_instance_ at runtime? I tried sth. like instance_eval and "class <<
self" which works. But do I add a mixin at runtime?

I have a Mixin like this:

Module B
  def B.append_features(aClass)
    def aClass.foo
      "foo"
    end
  end
end

o = Object.new
o.instance_eval<<-"end_eval"
  include B
end_eval

But o.foo does not exist!?

Is there a way to use append_features together with class<<self ?

-billy.
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