Showing a delegation pattern to handle fat models

user.rb

require 'forwardable'

class User

  extend Forwardable
  attr_accessor :view_delegate_class
  def_delegators :view_delegate, :full_name
  
  def initialize(first_name, last_name)
    @first_name = first_name  
    @last_name = last_name
  end   
  
  # if we set @view_delegate_class, we can override which class we use to show the full name
  # thus we can inject a dependency and at runtime choose the class to delegate to.
  def view_delegate
    (@view_delegate_class || UserViewDelegate).new(self)
  end
end

class UserViewDelegate

  def initialize(user)
    @user = user
  end 
  
  def full_name
    "#{first_name} #{last_name}"
  end
  
  # any method not defined here is going to be called on the @user.
  # normally, since these classes are extracted from larger classes, it saves us
  # having to say @user.first_name, @user.last_name, etc.
  # also, there it protects us from changes to the User class if we don't repeat the API here.
  def method_missing(name, *args)
    @user.send(name, *args)
  end   
  
end