Rails presenter base class.

gistfile1.rb

# app/presenters/presenter.rb

require "delegate"

class Presenter < SimpleDelegator
  attr_reader :model, :controller

  def initialize(model, controller)
    @controller = controller
    super(@model = model)
  end

end

gistfile2.rb

# app/presenters/user_presenter.rb

class UserPresenter < Presenter

  def render_errors
    # logic here ...
  
    controller.render_to_string(
      :partial => "/path/to/partial",
      :locals => { :model => self }
    )
  end

end

gistfile3.rb

# app/controllers/users_controller.rb

class UsersController < ApplicationController

  def new
    @user = UserPresenter.new(User.new, self)
  end

  def create
    user = User.new(user_params)
    if user.save
      redirect_to show_user_path(user)
    else
      @user = UserPresenter.new(user, self)
      render "new"
    end
  end

end

gistfile4.erb

<!-- app/views/users/new.html.erb -->

<%= @user.render_errors %>

<%= form_for @user ... do |f| %>
  ...
<% end %>

The pattern is simple and nice!