How do I wrap the invocation of a Ruby method by including a module?

Question

I want to be notified when certain things happen in some of my classes. I want to set this up in such a way that the implementation of my methods in those classes doesn\'t c

Answer 1

It has been quite a while since this question here has been active, but there is another possibility to wrap methods by an included (or extended) Module.

Since 2.0 you can prepend a Module, effectively making it a proxy for the prepending class.

In the example below, a method of an extended module module is called, passing the names of the methods you want to be wrapped. For each of the method names, a new Module is created and prepended. This is for code simplicity. You can also append multiple methods to a single proxy.

An important difference to the solutions using alias_method and instance_method which is later bound on self is that you can define the methods to be wrapped before the methods themselves are defined.

module Prepender

  def wrap_me(*method_names)
    method_names.each do |m|
      proxy = Module.new do
        define_method(m) do |*args|
          puts "the method '#{m}' is about to be called"
          super *args
        end
      end
      self.prepend proxy
    end
  end
end

Use:

class Dogbert
  extend Prepender

  wrap_me :bark, :deny

  def bark
    puts 'Bah!'
  end

  def deny
    puts 'You have no proof!'
  end
end

Dogbert.new.deny

# => the method 'deny' is about to be called
# => You have no proof!