Introduces design patterns and introduces the null object pattern, symptoms indicating it should be applied, a demonstration, and examples in popular Ruby gems

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