Blending Kotlin's culture into Swift

Transcript

1. Blending 
 Kotlin's culture into Swift 2017/8/9 ezura
2. “\(self)” ezura (@eduraaa) iOS engineer @LINE I like Swift :) I like Kotlin, Objective-C, …
3. Kotlin delegation object variance interface generics sealed
 class
4. sealed
 class Kotlin
5. index What is `sealed class`? blending `sealed class` concept into Swift trying it on a real product code
6. abstract
 class
 Super class
 SubA class
 SubB
7. when (instance as Super) { is SubA -> … // do something is SubB -> … // do something else -> … // fatal error? makeshift code? }.let { … } !!: Only when treating "when" as an expression, checked whether it covers all. switch-case
 expression noise… Kotlin
8. switch instance as Super { case let a as SubA: … // do something case let b as SubB: … // do something default: … // fatal error? makeshift code? } noise… Even if the premise is broken, 
 we can not detect statically. Swift Inhibit the representation 
 that it covers the whole type in the context :(
9. sad code… func didSelect(item: Item) { switch item { case let item as Book: // do something // use item as Book case let item as Memo: // do something // use item as Memo default: assertionFailure("unexpected type: \(item)") } } noise…
10. when (instance as Super) { is SubA -> … // do something is SubB -> … // do something else -> … // fatal error? makeshift code? }.let { … } !!: Only when treating "when" as an expression, checked whether it covers all. switch-case
 expression Kotlin
11. when (instance as Super) { is Super.SubA -> … // do something is Super.SubB -> … // do something else -> … // fatal error? makeshift code? }.let { … } noise… Kotlin !!: Only when treating "when" as an expression, checked whether it covers all.
13. sealed class
 Super class
 SubA class
 SubB
14. sealed class Super { // ... class SubA: Super() { // ... } class SubB: Super() { // ... } } Kotlin
15. when (instance as Super) { is Super.SubA -> … // do something is Super.SubB -> … // do something } Kotlin
16. Kotlin Beautiful world :)
17. Kotlin Swift Beautiful world :) sealed class
 concept
18. Goal not for:
 Completely reproducing the function of `sealed` for:
 reproducing the concept of `sealed` To clarify that the code covers the types 
 that can be taken in the context Swift
19. resolve this issue func didSelect(item: Item) { switch item { case let item as Book: // do something // use item as Book case let item as Memo: // do something // use item as Memo default: assertionFailure("unexpected type: \(item)") } } noise…
20. abstract
 class
 Item class
 Book class
 Memo protocol struct/enum struct/enum
21. protocol Item { // ... } struct Book: Item { // ... } struct Memo: Item { // ... } Swift
22. Cover all situations that may exist enum
23. enum ItemType { case book(Book) case memo(Memo) } Swift
24. func didSelect(item: ItemType) { switch item { case .book(let book): // do something // use item as Book case .memo(let memo): // do something // use item as Memo default: assertionFailure("unexpected type: \(item)") } } Swift noise…
25. protocol Item { // ... var name: String { get } } struct Book: Item { // ... let name: String } struct Memo: Item { // ... let name: String } Swift
26. let item: ItemType = … let name = item.name Swift error… enum ItemType { case book(Book) case memo(Memo) }
27. let name: String = { switch item { case .book(let book): return book.name case .memo(let memo): return memo.name } }() Swift
28. Kotlin :(
29. enum ItemType { case book(Book) case memo(Memo) } Swift Bad point: There is no (or weak) expression 
 that `enum ItemType` is a set of Sub types of “Item"
30. enum ItemType { // … private var base: Item { switch self { case .book(let item as Item),
 .memo(let item as Item): return item } } var name: String { return base.name } } Swift 3
31. enum ItemType: Item { // … private var base: Item { switch self { case .book(let item as Item),
 .memo(let item as Item): return item } } var name: String { return base.name } } Swift 3 or
32. enum ItemType: Item { // ... private var base: Item { switch self { case .book(let item): return item case .memo(let item): return item } } var name: String { return base.name } } Xcode 9.0 beta 4
33. enum ItemType { case book(Book) case memo(Memo) private var base: Item { switch self { case .book(let item as Item),
 .memo(let item as Item): return item } } var name: String { return base.name } } Swift result
34. func didSelect(item: ItemType) { switch item { case .book(let book): // do something // use item as Book case .memo(let memo): // do something // use item as Memo default: assertionFailure("unexpected type: \(item)") } } Swift noise…
35. Swift protocol Item { // ... var name: String { get } } let item: ItemType = … let name = item.name
36. Appendix
37. In refactoring,
 we Partially incorporate similar concept
38. class SampleController { var item: Item // … func f() { switch item { case let item as Book: // do something // use item as Book case let item as Memo: // do something // use item as Memo default: assertionFailure("unexpected type: \(item)") } } } Swift before
39. class SampleController { enum ItemType { case book(Book) case memo(Memo) private var base: Item { … } // … } var item: ItemType func f() { … } } // usage SampleController(item: .book(book)) SampleController(item: .memo(memo)) Swift after
40. Conclusion blending Kotlin's “sealed class concept” into Swift We can express the context clearly with the above concept We can partially try this
41. Thank you 
 for listening