The document discusses the null object pattern, a behavioral design pattern that serves as a reusable solution to common problems in software design. It highlights its application in computer science since 1987 and provides examples of where it can be used, such as in various code libraries. Additional resources for further reading on the topic are also mentioned.

1. Null Object Pattern
Simplicity in doing nothing

2. What is a Design Pattern?
● A reusable solution to a common problem
● Kent Beck and Ward Cunningham applied to
computer science in 1987
● Defined in Design Patterns: Elements of
Reusable Object-Oriented Software by GoF

3. Null Object Pattern
● Categorized as behavioral pattern
● Similar to the strategy, or state pattern
● Polymorphism
● null interface that can be used by a
collaborator

4. When To Use
● Symptoms include null checks on properties
● Conditional logic to display an object
● Use of a placeholder

5. Demo

6. ● Bespoke: lib/search/solr/empty_result_set.rb
● Cheetah:
lib/cheetah/messenger/null_messenger.rb
● Display_case: lib/display_case/exhibit.rb
(null decorator)
● Factory_girl: lib/factory_girl/null_factory.rb
Examples in our Code

7. Extra Reading
Blog post on Factory Girl NullFactory class:
http://robots.thoughtbot.com/design-patterns-in-
the-wild-null-object