SOLID principles

The principles when applied together intend to create a system
that is easy to maintain and extend over time.
It is typically used with test-driven development,
and is part of an overall strategy of agile and adaptive programming.

Transcript

1. SOLID SOLID Tien Le The East Agile Team Hi!
2. The principles when applied together intend to create a system The principles when applied together intend to create a system that is easy to maintain and extend over time. that is easy to maintain and extend over time. It is typically used with test-driven development, It is typically used with test-driven development, and is part of an overall strategy of agile and adaptive programming. and is part of an overall strategy of agile and adaptive programming. Wikipedia.org Wikipedia.org
3. S SOLID OLID Single Responsibility Single Responsibility
4. Single Responsibility Principle Single Responsibility Principle “ “A class should have one, and only one, A class should have one, and only one, reason to change (responsibility) reason to change (responsibility)” ” - Uncle Bob - Uncle Bob “ “do one thing well” - Unix philosophy do one thing well” - Unix philosophy
5. class class Scraper Scraper def initialize def initialize end end // input // input def fetch_data def fetch_data end end // process // process def parse def parse End End // ouput // ouput def to_s def to_s End End // store // store def save def save end end end end class class Scraper Scraper include Scraper::Fetchable include Scraper::Fetchable include Scraper::Parsable include Scraper::Parsable include Scraper::Printable include Scraper::Printable Include Scraper::Persistable Include Scraper::Persistable def initialize; end def initialize; end end end
6. S SO OLID LID Open/Closed Principle Open/Closed Principle
7. Open/Closed Principle Open/Closed Principle “ “You should be able to extend a class behavior You should be able to extend a class behavior without modifying it” without modifying it” - Uncle Bob - Uncle Bob
8. Open/Closed Principle Open/Closed Principle "Favor ' "Favor 'object composition object composition' over ' ' over 'class inheritance'. class inheritance'." " (Gang of Four 1995:20) (Gang of Four 1995:20) E.g: Rspec matchers, ActiveRecord validators, … E.g: Rspec matchers, ActiveRecord validators, … class Person class Person Include ActiveModel::Validation Include ActiveModel::Validation validates_with validates_with HasNameValidator HasNameValidator End End RSpec::Matchers RSpec::Matchers.define :be_a_multiple_of do |expected| .define :be_a_multiple_of do |expected| match do |actual| match do |actual| actual % expected == 0 actual % expected == 0 end end end end expect(9).to be_a_multiple_of(3) expect(9).to be_a_multiple_of(3)
9. SO SOL LID ID Liskov Subtitution Liskov Subtitution
10. Liskov Subtitution Principle Liskov Subtitution Principle “ “Derived classes must be substitutable Derived classes must be substitutable for their base class” for their base class” - Uncle Bob - Uncle Bob
11. SOL SOLI ID D Interface Segregation Interface Segregation
12. Interface Segregation Principle Interface Segregation Principle “ “Many client specific interfaces Many client specific interfaces are better than one general purpose interface” are better than one general purpose interface”
13. SOLI SOLID D Dependency Inversion Dependency Inversion
14. Dependency Inversion Principle Dependency Inversion Principle “ “Depend on abstractions, not on concretions” Depend on abstractions, not on concretions” - Uncle Bob - Uncle Bob
15. class Scraper class Scraper def to_s def to_s PrettyPrinter PrettyPrinter.print(self) .print(self) end end End End class Scraper class Scraper def to_s(printer = def to_s(printer = PrettyPrinter PrettyPrinter) ) printer printer.print(self) .print(self) end end end end
16. Some stuffs in this slide are from: Agile Software Development, Principles, Patterns, and Practices – Rober C. Martin aka “Uncle Bob” https://speakerdeck.com/plataformatec/rails-solid-by-jose-valim-railsconf-2011 Thank you Happy coding ;-) Thank you Happy coding ;-)