countable.rb

# TODO: Cómo hago que funcione con métodos que reciben parámetros?
# Referencia: http://www.railstips.org/blog/archives/2009/05/15/include-vs-extend-in-ruby/

module Countable
  module ClassMethods
    def count_invocations_of(sym)
      alias_method "original_#{sym}".to_sym, sym

      define_method(sym) do
        start_counter
        @invocations[sym] += 1
        send("original_#{sym}")
      end
    end
  end

  # Module#included hook
  def self.included(includer)
    includer.extend(ClassMethods)
  end

  def invoked?(sym)
    start_counter
    @invocations[sym] > 0
  end

  def invoked(sym)
    start_counter
    @invocations[sym]
  end

  private

  def start_counter
    @invocations ||= Hash.new(0)
  end
end

# Ejemplo de uso de Countable
class Greeter
  # Incluyo el Mixin
  include Countable

  def hi
    puts 'Hey!'
  end

  def bye
    puts 'See you!'
  end

  # Indico que quiero llevar la cuenta de veces que se invoca el método #hi
  count_invocations_of :hi
end

a = Greeter.new
b = Greeter.new

a.invoked? :hi
# => false
b.invoked? :hi
# => false

a.hi
# Imprime "Hey!"

a.invoked :hi
# => 1
b.invoked :hi
# => 0