From: Chuck Remes <cremes.devlist@...>
Date: 2010-08-12T00:32:56+09:00
Subject: injecting an instance method into another class' class method

I'd like to reopen a class Foo and redefine one of its methods to use an instance method from class Bar. I can't seem to figure out how to do it or even if it is possible.

I tried lots of different techniques and none have worked, so here I am asking for a bit of help. An example of one of the techniques I tried is included below.

class Foo
  def self.now
    Time.now.to_i
  end
end

class Bar
  def initialize
    @bar = proc { now }

    Bar.class_eval <<-code
    class Foo
      def Foo.now
        @bar.call
      end
    end
    code
  end

  def now
    puts "bar now called"
  end
end


I would like Foo.now to return Time.now.to_i for the normal case. However, after an instance of Bar is created, I would like the Bar instance to redefine Foo.now to call the #now instance method of Bar.

This is what the output should look like:

ruby-1.9.1-p378 > Foo.now
 => 1281540640 
ruby-1.9.1-p378 > Bar.new
bar now
 => #<Bar:0x00000101216268 @bar=#<Proc:0x000001012161c0@(irb):41>> 
ruby-1.9.1-p378 > Foo.now
 => "bar now called"


Is it possible to do this?

cr