Ruby multiple callbacks

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 Callbacks
  def initialize(block)
    block.call(self)
  end

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

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

  private

  def callbacks
    @callbacks ||= {}
  end
end

class Twitter
  def tweet(msg, &block)
    callbacks = Callbacks.new(block)
    publish(msg)
    callbacks.callback(:success)
  rescue => e
    callbacks.callback(:failure, e.message)
  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

For n00bs like myself who are trying to practice the dark art of Procs, the key component at play is the #method_missing piece. This will register the callback (on.success, on.failure) as a symbolized key in the @callbacks hash, but only once.

A similar solution would be to define methods success and failure on the Twitter class. For those new to experimenting with Procs, this solution may work a little better as the code path is a little more transparent.

Thanks for this tacit and well crafted example!