How to implement a “callback” in Ruby?

Question

I\'m not sure of the best idiom for C style call-backs in Ruby - or if there is something even better ( and less like C ). In C, I\'d do something like:

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Answer 1

So, this may be very "un-ruby", and I am not a "professional" Ruby developer, so if you guys are going to smack be, be gentle please :)

Ruby has a built-int module called Observer. I have not found it easy to use, but to be fair I did not give it much of a chance. In my projects I have resorted to creating my own EventHandler type (yes, I use C# a lot). Here is the basic structure:

class EventHandler

  def initialize
    @client_map = {}
  end

  def add_listener(id, func)
    (@client_map[id.hash] ||= []) << func
  end

  def remove_listener(id)
    return @client_map.delete(id.hash)
  end

  def alert_listeners(*args)
    @client_map.each_value { |v| v.each { |func| func.call(*args) } }
  end

end

So, to use this I expose it as a readonly member of a class:

class Foo

  attr_reader :some_value_changed

  def initialize
    @some_value_changed = EventHandler.new
  end

end

Clients of the "Foo" class can subscribe to an event like this:

foo.some_value_changed.add_listener(self, lambda { some_func })

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I am sure this is not idiomatic Ruby and I am just shoehorning my C# experience into a new language, but it has worked for me.