Protocol and Value Oriented Programming

By Jerry

Transcript

1. Protocol and Value
 Oriented Programming A new programming paradigm with Swift? @jerry.ko
2. What is Protocol?
3. A protocol defines a blueprint of requirements that suit a particular task or piece of functionality. The protocol can then be adopted by a class to provide an actual implementation of those requirements. You can inherit a protocol to build a hierarchy of protocols and to add more requirements.
4. protocol == interface?
5. A protocol defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality. The protocol can then be adopted by a class, structure, or enumeration to provide an actual implementation of those requirements. You can inherit a protocol to build a hierarchy of protocols and to add more requirements. In addition, you can extend a protocol to implement some of these requirements.
6. A protocol defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality. The protocol can then be adopted by a class, structure, or enumeration to provide an actual implementation of those requirements. You can inherit a protocol to build a hierarchy of protocols and to add more requirements. In addition, you can extend a protocol to implement some of these requirements.
7. Property/method requirements for class/struct/enum protocol FullyNamed { var fullName: String { get } func printFullName() } class Cat: FullyNamed { var fullName: String func printFullName() { print(“A cat named \(fullName)") } } struct Person: FullyNamed { var fullName: String func printFullName() { print(“A person named \(fullName)") } } protocol Togglable { mutating func toggle() } enum OnOffSwitch: Togglable { case off, on mutating func toggle() { switch self { case .off: self = .on case .on: self = .off } } }
8. Protocol with Extension struct Car { let year: Int let modelName: String ... } extension Car: FullyNamed { var fullName: String { return "\(year) \(modelName)" } } Adopting Protocol Retroactively protocol FullyNamed { var fullName: String { get } func printFullName() } extension FullyNamed { func printFullName() { print("It's name is \(fullName)") } } Providing Default Implementation
9. Conditional Protocol Adoption extension Array: TextRepresentable where Element: TextRepresentable { var textualDescription: String { let itemsAsText = self.map { $0.textualDescription } return "[" + itemsAsText.joined(separator: ", ") + "]" } }
10. What’s Wrong with Inheritance?
12. Inheritance, OOP One superclass — choose well! No retroactive modeling Superclass may have stored properties • You must accept them • Initialization burden Should know what/how to override (and when not to)
13. Protocol in Action
14. class Ordered { func precedes(other: Ordered) -> Bool { fatalError("implement me!") } } class Number: Ordered { var value: Double = 0 override func precedes(other: Ordered) -> Bool { return value < (other as! Number).value } }
15. class Ordered { func precedes(other: Ordered) -> Bool { fatalError("implement me!") } } class Number: Ordered { var value: Double = 0 override func precedes(other: Ordered) -> Bool { return value < (other as! Number).value } }
17. protocol Ordered { func precedes(other: Self) -> Bool } class Number: Ordered, Printable, ... { var value: Double = 0 func precedes(other: Number) -> Bool { return self.value < other.value } }
19. protocol ViewWithBorder { var borderColor: UIColor { get } var borderThickness: CGFloat { get } init(borderColor: UIColor, borderThickness: CGFloat, frame: CGRect) } extension ViewWithBorder where Self: UIView { func addBorder() -> Void { layer.borderColor = borderColor.cgColor layer.borderWidth = borderThickness } } extension UIButton: ViewWithBorder {} extension UIImageView: ViewWithBorder {} button.addBorder() imageView.addBorder()
20. Don’t start with a class. 
 Start with a protocol!
21. Reference vs. Value
22. Problems with Reference ?
23. Problems with Reference Unintended Sharing
24. Implicit Sharing, the Root of Bugs! Mutation Race Condition Locks Complexity Ineffiency
25. How to deal with it?
26. Manual Copying
27. Defensive Copying
28. Eliminating Mutation
29. Eliminating Mutation
30. Value Semantics
31. Variables are Logically Distinct Value Types are Distinguished by Value
32. Values are Copied. Performance with all the copies?
33. Copies are Cheap
34. In Swift,
35. Value Type in Action
36. Implementing Undo
37. Implementing Undo
38. Implementing Undo
39. class? struct? Then, struct!
40. So, POP with Value Semantics is 
 the Future of Programming Language?
41. Composition over Inheritance?
42. Mixing Value Types and Reference Types Maintaining value semantics requires special considerations! • How do we cope with mutation of the referenced object? • How does the reference identity affect equality? Unrestricted mutation of referenced objects breaks value semantics. • Non-mutating operations are always safe • Mutating operations must first copy
43. However,
44. TIOBE Index for October 2018
45. Swift is the latest language that is already popular and backed up by giant brother, Apple. So, it’s worth having POP and Value Semantics in mind!
46. Thank you