Nothing and Ducks

Types of Nothing in Code

0.0 / 0.0 # => NaN

""

[]

{}

nil

NaN is a Duck

def math_it_up!(number)
  number * 100 / 10 + 5 - 3
end

math_it_up!(2)       # => 22
math_it_up!(0.0/0.0) # => NaN

"" is a Duck

def string_it_up!(string)
  string.upcase.capitalize
end

string_it_up!("ducks") # => "Ducks"
string_it_up!("")      # => ""

[] and {} are Ducks

def array_it_up!(array)
  array.map(&:to_s)
end

array_it_up!([1, 2]) # => ["1", "2"]
array_it_up!([])     # => []

def hash_it_up!(hash)
  hash.group_by(&:last).map{|num, pairs| [num, pairs.map(&:first)]}
end

hash_it_up!(:one => 1, :uno => 1, :dos => 2, :two => 2)
  # => [[1, [:uno, :one]], [2, [:dos, :two]]]
hash_it_up!({}) # => []

nil is a Goose

class Report
  def initialize(data)
    @data = data
  end 
  def generate
    @data.each do |row|
      puts row
    end    @generated = true
  end
end

report = Report.new([1, 3, 6])
report.generate

nil.generate # => NoMethodError: undefined method `generate' for nil:NilClass

Overcoming Object Nothingness

Real World Example

module Emails
  class EmailDirector
    class << self
      def get_email_for(email_type)
        "Emails::EmailTypes::#{email_type.classify}".constantize.new 
      rescue NameError
        nil
      end
    end
  end
end

Real World Example

class MessageDispatcher
  class << self
    def method_missing(method, *args)
      email = EmailDirector.get_email_for(method, *args)
      
      if email && email.use_exact_target?
        email.push_email_message_to_bus
      else
        CustomerNotifier.send(method, *args)
      end
    end
  end
end

Real World Example

class Emails::EmailTypes::Base
  def initialize(*args); raise "Me wants initialization"; end
  def use_exact_target?; raise "Me wants definition"; end
      
  def push_email_message_to_bus
    xml = build_message
    push_message_to_bus(xml)
  end

private

  def build_message; raise "Me wants definition"; end
      
  def push_message_to_bus(xml)
    ESB::MessageBridge.transaction do
      ESB::MessageBridge.push(xml, :mail_message)
    end
  end   
end

Real World Example

module Emails
  module EmailTypes
    class NilType < Emails::EmailTypes::Base
      def initialize(*args)        
      end
      
      def use_exact_target?
        false
      end
            
    private  
      
      def build_message
      end
    end
  end
end

Real World Example

module Emails
  class EmailDirector
    class << self
      def get_email_for(email_type, *args)
        "Emails::EmailTypes::#{email_type.camelize}".constantize.new(*args)
      rescue NameError
        Emails::EmailTypes::NilType.new
      end
    end
  end
end

Real World Example

class MessageDispatcher
  class << self
    def method_missing(method, *args)
      email = EmailDirector.get_email_for(method, *args)
      
      if email.use_exact_target?
        email.push_email_message_to_bus
      else
        CustomerNotifier.send(method, *args)
      end
    end
  end
end

Generalizing the Null Object Pattern

Generalizing the Null Object Pattern

Generalizing the Null Object Pattern

class NullObject
  def initialize(*args)
  end
  
  def method_missing(*args)
  end
end

object = NullObject.new
object.do_important_stuff!