hexagonal_eg.rb

class Broadcaster < Struct.new( :listeners )
  def broadcast( message, *args )
    listeners.each { |listener| listener.send( message, *args ) }
  end
end

module Services
  class ItemCreate < Broadcaster
    def initialize( params, *listeners )
      super( listeners )
      @params = params
    end

    def create
      item = Item.create( params )
      item.save ?
        broadcast( :item_created, item ) :
        broadcast( :item_create_failed, item )
    end

    private
    attr_accessor :params
  end
end

module Responders
  class ItemCreate < SimpleDelegator
    def item_created( item )
      flash[:notice] = "The item has been created"
      redirect_to( item_path( item ) )
    end

    def item_create_failed( item )
      flash[:error] = "That all went horribly wrong"
      render( "new", :locals => { :item => item } )
    end
  end
end

class ItemController < ApplicationController
  def new
    render( "new" )
  end
  
  def create
    Services::ItemCreate.new( params, Responders::ItemCreate.new( self ) ).create
  end
end