Hooks and callbacks for Ruby. But simple.

Callbacks are executable things, like a Proc or methods in Ruby, whereas a hook is usually a spot in your code where you want to execute a certain subset of callbacks.

Or, precisely, callbacks that are associated to the hook.

I have lots of these places throughout my libraries, and after playing around with ActiveSupport::Callbacks (both 2.3 and 3.0) I wrote a minimal gem to do exactly that:

Declaratively define hooks, add callbacks and run them with the options you like.

Let’s see how it works. First, install hooks.

$ gem install hooks

Using hooks

Usually you’d define hooks declaratively in your class.

class Coder
  include Hooks
    
  define_hook :after_work

You’re now ready to add callbacks, as your class now has a Class.after_work method. Nothing more.

class Coder
  after_work do
    puts "Yeah!"
  end

Instance methods are also callback’able.

  after_work :have_a_beer
  
  def have_a_beer
    puts "One for me, one for Michał!"
  end

Now, run a hook somewhere in your code.

  def finish
    cleanup!
    run_hook :after_work
  end

The callbacks will be invoked in the order you added them. Sweet.

Running a hook with arguments

If you need objects in your callbacks, just pass ’em.

    run_hook :at_work, self, Time.now

And be sure to equip your callbacks with the right parameters.

  at_work do |who, when| ... end

Filters?

So, basically a filter as found in Rails controllers is a hook. You – the user – use Controller.after_login to add callbacks. And somewhere in the Rails core, there’d be a call to

  run_hook :after_login, self

…if they’d be using hooks.

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