01-trips_controller.rb

class TripsController < ApplicationController
  class Action < ApplicationController::Action
  end

  class New < Action
    expose(:trip) { Trip.new(params[:trip]) }
  end

  class Create < New
    def call
      CreateTrip.new(self).execute(current_user, params[:trip])
    end

    def successful(trip)
      redirect_to trip
    end

    def failed(trip)
      render :action => :new
    end
  end
end

02-create_trip.rb

class CreateTrip

  def initialize(listener)
    @listener = listener
  end

  def execute(user, attributes)
    trip = Trip.new(attributes)
    trip.user = user
    if trip.save
      listener.successful(trip)
    else
      listener.failed(trip)
    end
  end

  private

  attr_reader :listener
end