Presenter pattern for Rails 2 apps

application_helper.rb

# -*- encoding: utf-8 -*-

# app/helpers/application_helper.rb

module ApplicationHelper

  # code...

  def present(object, klass = nil)
    presenter = ::BasePresenter.build(object, self, klass)

    yield presenter if block_given?

    presenter
  end
end

base_presenter.rb

# -*- encoding: utf-8 -*-

# app/presenters/base_presenter.rb

class BasePresenter

  class << self
    def presents(name)
      define_method(name) do
        @object
      end
    end

    def build(object, view, klass = nil)
      klass ||= "#{object.class.name}Presenter".constantize

      klass.new(object, view)
    end
  end

  def initialize(object, view)
    @object = object
    @view   = view
  end

  def h
    @view
  end
  protected :h
end

base_presenter_test.rb

# -*- encoding: utf-8 -*-

# test/unit/presenters/base_presenter_test.rb

require 'test_helper'
require File.expand_path(File.dirname(__FILE__) + "/presenter_test_case")

class Example; end

class ExamplePresenter < BasePresenter
  presents :example
end

class BasePresenterTest < PresenterTestCase
  setup :prepare_presenter

  test "should build the associated presenter" do
    assert @presenter.is_a?(ExamplePresenter)
  end

  test "should access the presented object by its name" do
    assert @presenter.respond_to?(:example)
    assert_equal @example, @presenter.example
  end

  private

  def prepare_presenter
    @example   = Example.new
    @presenter = BasePresenter.build(@example, view)
  end
end

post_presenter.rb

# -*- encoding: utf-8 -*-

# app/presenters/post_presenter.rb

# Example Presenter for the Post model.
class PostPresenter < BasePresenter
  presents :post
  delegate :title, :to => :post

  def linked_title
    h.link_to post.title, post
  end

  # code ...
end

presenter_test_case.rb

# -*- encoding: utf-8 -*-

# test/unit/presenters/presenter_test_case.rb

require 'test_helper'

class PresenterTestCase < ActiveSupport::TestCase
  private

  def view
    @view ||= build_view
  end

  def build_view
    klass = Class.new do
      class << self
        def helpers_dir
          "#{Rails.root}/app/helpers"
        end

        def all_application_helpers
          extract = /^#{Regexp.quote(helpers_dir)}\/?(.*)_helper.rb$/
          Dir["#{helpers_dir}/**/*_helper.rb"].map { |file| file.sub extract, '\1' }
        end
      end

      all_application_helpers.each do |helper|
        file_name  = helper.to_s.underscore + '_helper'
        class_name = file_name.camelize

        require_dependency file_name

        include class_name.constantize
      end
    end

    klass.new
  end
end

show.html.erb

<%# app/views/posts/show.html.erb %>
<% present @post do |presenter| %>
  <h2><%= presenter.linked_title %></h2>
<% end %>

Based on the Ryan Bate's work: http://railscasts.com/episodes/287-presenters-from-scratch