Module to wrap a class method?

Question

Is it possible to make this work, without having to include the module at the end of the class and just include it at the top?

module VerboseJob
  def self.included(job_class)
    class << job_class
      alias_method :original_perform, :perform
      def perform(*args)
        JobLogger.verbose { original_perform(*args) }
      end
    end
  end
end

class HelloJob
  include VerboseJob

  def self.perform(arg1, arg2)
    puts "Job invoked with #{arg1} and #{arg2}"
  end
end

What I want to happen, is for HelloJob.perform to actually invoke VerboseJob.perform (which then calls the original method inside a block). Because the module here is included at the top of the class, this doesn't work, since perform isn't yet defined. Moving the include to the end does work, but is there a way that's a bit more forgiving? I like to keep all the included modules at the top of my class definitions.

I'm sort of looking for some method that is called on Module or Class when it has been fully loaded, instead of as it is interpreted by the runtime.

Answer 1

Here is a rather roundabout/hackish way of doing it that I came up with by deferring the definition of the wrapper method until the original method had been defined:

module A
  def self.included(base)
    base.class_eval do
      def self.singleton_method_added(name)
        @@ran||=false
        if name==:perform && !@@ran
          @@ran=true
          class<<self
            alias_method :original_perform, :perform
            def perform(*args)
              puts "Hello"
              original_perform(*args)
            end
          end
        end
      end
    end
  end
end

class B
  include A

  def self.perform
    puts "Foobar"
  end
end

B.perform

Edit:

d11wtq simplified this to the much cleaner:

module VerboseJob
  module ClassMethods
    def wrap_perform!
      class << self
        def perform_with_verbose(*args)
          JobLogger.verbose { perform_without_verbose(*args) }
        end

        alias_method_chain :perform, :verbose \
          unless instance_method(:perform) == instance_method(:perform_with_verbose)
      end
    end

    def singleton_method_added(name)
      wrap_perform! if name == :perform
    end
  end

  def self.included(job_class)
    job_class.extend ClassMethods
    job_class.wrap_perform! if job_class.respond_to?(:perform)
  end
end