Basic Null Object for use in the Rubies

nullobject.rb

# A simple null object
class NullObject < BasicObject
  def to_ary; nil end # Handle the `puts call to_ary` don't ask

  # Add the attributes, methods you care to define here
  # ...
  #
  # def name
  #   'Nully'
  # end

  # Let method missing handle the rest
  def method_missing(name, *args, &block) 
    name_str = name.to_s
    case 
    when name_str.end_with?('?') 
      false
    when name_str.end_with?('s')
      []
    else
      self
    end
  end
end


nully = NullObject.new
nully.nullies?  # false
nully.nullify!  # self
nully.nullies.empty? # true
nully.some_association? # false
nully.some_association.optimistic.call # self
nully.nullies.each { |x| foo(x) }  # nil


#
# Rails Example
#

class User < ActiveRecord::Base
  has_many :campaigns
end

class Guest < NullObject
  def campaigns # Expose ActiveRelation methods
    Campaign.none
  end
end

class CampaignTrafficker
  def initialize(user: nil)
    @user = user || Guest.new # protect against explicity passing falsy user argument
  end

  def send_campaigns!
    user.campaigns.each { |campaign| campaign.traffic! }
  end

  private

  attr_internal_reader :user
end

CampaignTrafficker.new(user: User.first).send_campaigns! # might do something
CampaignTrafficker.new(user: nil).send_campaigns! # won't do anything do something

#
# Null objects w/ duck typing 
#

# No more!

foo && foo.bar

if foo
  bar
end

foo.try(:bar).try(:name)

#
# Ditch the IFs Use NullObjects w/ Duck-Typing
#