- Boolean data type
- Don't repeat yourself – O'Reilly
- DRY: Don't Repeat Yourself
- Edge case
- Extract Class on Scrutinizer
- Extract Class on SourceMaking
- Polymorphism and Duck Typing
- Refactoring book
- Refactoring
- Class Extraction
- Single Responsibility Principle
- SOLID principles
- TDD on Wikipedia
- Web Developer Roadmap
- Ruby Array
- Ruby Arrays on RubyMonk
- Ruby constants
- Ruby Docs - Exception (Ruby's name for 'error')
- Ruby Hash
- Ruby Hashes on RubyMonk
- Ruby instance variables and accessors
- Ruby instance variables
- Ruby's guide to symbols
- RubyGems basics
- RubyMonk
- RVM documentation
- Writing your own classes in Ruby
- True, False and Nil
- If statements
- Gemfile documentation on bundler.io
- Bundler documentation
- Handling and Raising exceptions
- What is a Gemfile
- String interpolation
- Modules on Pragmatic Programmers
- Modules on RubyMonk
- Modules: Learn Ruby the Hard Way
- Including other files in Ruby
- Predicate methods