Alternative to modifying Proc directly

gistfile1.rb

# alternative to what is explained in the article Ruby Blocks as Dynamic Callbacks: 
# http://www.mattsears.com/articles/2011/11/27/ruby-blocks-as-dynamic-callbacks

class Twitter
  def tweet(msg, &block)
    proxy = DSL[block]
    publish(msg)
    proxy.respond_with(:success)
  rescue => e
   proxy.respond_with(:failure, e.message)
  end

  class DSL
    def self.[](block)
      new.tap { |proxy| block.call(proxy) }
    end

    def respond_with(callback, *args)
      callbacks[callback].call(*args)
    end

    def method_missing(m, *args, &block)
      block ? callbacks[m] = block : super
      self
    end

    private

    def callbacks
      @callbacks ||= {}
    end
  end
end

t = Twitter.new
t.tweet('Hello there!') do |on|
  on.success do
    puts "Success!"
  end

  on.failure do |msg|
    puts "Failure! Message: #{msg}"
  end
end