Presenter Design Pattern (without double iterating when coming from #index)

presenter_design_pattern.rb

# app/controllers/pets_controller.rb
class PetsController < ApplicationController
  before_action :set_pet, only: [:show, :edit, :update, :destroy]

  def index
    # old way
    # @pet_presenters = Pet.all.map { |pet| PetPresenter.new(pet, view_context) }
    
    # new way
    @pet_presenters = PetsPresenter.prepare(Pet.all, view_context)
  end

  def show
    @pet_presenter = PetPresenter.new(Pet.find(params[:id]))
  end
end

# app/presenters/pets_presenter.rb
class PetsPresenter
  
  attr_reader :pets, :view_context
  def initializer pets, view_context
    @pets = pets
    @view_context = view_context
  end
  
  def self.each
    pets.each do |pet|
      yield PetPresenter.new(pet, view_context)
    end
  end
end

class PetPresenter < SimpleDelegator
  attr_reader :pet
  attr_accessor :view_context

  def initialize(pet, view_context)
    super(pet)
    @view_context = view_context
  end

  def display_name
    view_context.link_to "#{name} the #{breed}", self
  end
end

# app/views/pets/index.html.erb
<% @pet_presenters.each do |pet| %>
  <tr>
    <td><%= pet.display_name %></td>
    <td><%= link_to 'Show', pet %></td>
    <td><%= link_to 'Edit', edit_pet_path(pet.id) %></td>
    <td><%= link_to 'Destroy', pet, method: :delete, data: { confirm: 'Are you sure?' } %></td>
  </tr>
<% end %>