presenter.rb

class ActionController::Presenter
  attr_reader :controller, :request, :format, :resource, :resource_location

  def initialize(controller, resource)
    @controller = controller
    @request = controller.request
    @format = controller.formats.first

    @resource = resource.is_a?(Array) ? resource.last : resource
    @resource_location = resource
  end

  delegate :head, :render, :redirect_to,   :to => :controller
  delegate :get?, :post?, :put?, :delete?, :to => :request

  # Undefine :to_json since it's defined on Object
  undef_method :to_json

  def to_html
    if get?
      render
    elsif has_errors?
      render :action => default_action
    else
      redirect_to resource_location
    end
  end

  def to_format
    return render unless resourceful?

    if get?
      render format => resource
    elsif has_errors?
      render format => resource.errors, :status => :unprocessable_entity
    elsif post?
      render format => resource, :status => :created, :location => resource_location
    else
      head :ok
    end
  end

  def resourceful?
    resource.respond_to?(:"to_#{format}")
  end

  def has_errors?
    resource.respond_to?(:errors) && !resource.errors.empty?
  end

  def default_action
    request.post? ? :new : :edit
  end
end

scaffold_with_presenter.rb

# Scaffold with presenter
class UsersController < ApplicationController
  respond_to :html, :xml

  # GET /users
  # GET /users.xml
  def index
    @users = User.all
    respond_with(@users)
  end

  # GET /users/1
  # GET /users/1.xml
  def show
    @user = User.find(params[:id])
    respond_with(@user)
  end

  # GET /users/new
  # GET /users/new.xml
  def new
    @user = User.new
    respond_with(@user)
  end

  # GET /users/1/edit
  def edit
    @user = User.find(params[:id])
    respond_with(@user)
  end

  # POST /users
  # POST /users.xml
  def create
    @user = User.new(params[:user])
    flash[:notice] = 'User was successfully created.' if @user.save
    respond_with(@user)
  end

  # PUT /users/1
  # PUT /users/1.xml
  def update
    @user = User.find(params[:id])
    flash[:notice] = 'User was successfully created.' if @user.update_attributes(params[:user])
    respond_with(@user)
  end

  # DELETE /users/1
  # DELETE /users/1.xml
  def destroy
    @user = User.find(params[:id])
    @user.destroy
    respond_with(@user)
  end
end