iOS Dev Meetup. Emelyanov Georgij - Collectionsunderhood

Transcript

1. COLLECTIONS UNDER HOOD
2. COLLECTIONSUNDERHOOD Array Set Dictionary String Range AnyCollection EmptyCollection FlattenCollection ClosedRange LazyCollection ContiguousArray ArraySlice 2 Slice CollectionOfOne LazyMapCollection ReversedCollection
3. COLLECTIONSUNDERHOOD Agenda ▸ Protocols Hierarchy ▸ Array(s), Dictionary, Set ▸ Objective-C Heritage 3
4. PROTOCOLS HIERARCHY 4
5. COLLECTIONSUNDERHOOD Sequence SomeCollection Collection Equatable Decodable Encodable Hashable CustomDebugStringConvertible CustomReflectable CustomStringConvertible 5
6. A sequence is a list of values that you can step through one at a time. A type that provides sequential, iterated access to its elements Apple’s Doc COLLECTIONSUNDERHOOD Sequence 6
7. COLLECTIONSUNDERHOOD let confs = [...] for conf in confs { print(conf) } // Behind the scenes var iterator = confs.makeIterator() while let conf = iterator.next() { print(conf) } 7
8. COLLECTIONSUNDERHOOD protocol Sequence { associatedtype Iterator: IteratorProtocol func makeIterator() -> Iterator } Sequence 8
9. COLLECTIONSUNDERHOOD protocol IteratorProtocol { associatedtype Element mutating func next() -> Element? } IteratorProtocol 9
10. COLLECTIONSUNDERHOOD IteratorProtocol mutating func next() -> Elements.Element? { if _position == _elements.endIndex { return nil } let element = _elements[_position] _elements.formIndex(after: &_position) return element } 10
11. COLLECTIONSUNDERHOOD func filter(_:) func forEach(_:) func map(_:) func compactMap(_:) func contains(_:) func dropFirst(_:) func dropLast(_:) func prefix(_:) func suffix(_:) ... Sequence 11
12. COLLECTIONSUNDERHOOD func count(where condition: (Element) throws -> Bool) rethrows -> Int { var count = 0 for element in self where try condition(element) { count += 1 } return count } Sequence 12
13. In addition to the operations that collections inherit from the Sequence protocol, you gain access to methods that depend on accessing an element at a specific position in a collection. Apple’s Doc COLLECTIONSUNDERHOOD Collection 13
14. COLLECTIONSUNDERHOOD var count: Int var endIndex: Self.Index var first: Self.Element? var indices: Self.Indices var isEmpty: Bool var startIndex: Self.Index subscript(_: Self.Index) subscript(_: Range<Self.Index>) ... Collection 14
15. COLLECTIONSUNDERHOOD let products: [Category : [Product]] = [ .dairy: [ Product(name: "Milk", category: .dairy), Product(name: "Butter", category: .dairy) ], .vegetables: [ Product(name: "Cucumber", category: .vegetables), Product(name: "Lettuce", category: .vegetables) ], ... ] 15
16. COLLECTIONSUNDERHOOD func add(_ product: Product) { if var productsInCategory = products[product.category] { productsInCategory.append(product) products[product.category] = productsInCategory } else { products[product.category] = [product] } } 16
17. COLLECTIONSUNDERHOOD if let dairyProducts = products[.dairy] { guard !dairyProducts.isEmpty else { renderEmptyView() return } render(dairyProducts) } else { renderEmptyView() } 17
18. COLLECTIONSUNDERHOOD struct ProductCollection { typealias DictionaryType = [Category : [Product]] private var products = DictionaryType() init(products: DictionaryType) { self.products = products } } 18
19. COLLECTIONSUNDERHOOD extension ProductCollection: Collection { var startIndex: Index { return products.startIndex } var endIndex: Index { return products.endIndex } subscript(index: Index) -> Iterator.Element { get { return products[index] } } func index(after i: Index) -> Index { return products.index(after: i) } } 19
20. COLLECTIONSUNDERHOOD for (category, productsInCategory) in products { ... } 20
21. COLLECTIONSUNDERHOOD 21 let categories = productCollection.map { $0.key }
22. COLLECTIONSUNDERHOOD subscript(category: Category) -> [Product] { get { return products[category] ?? [] } set { products[category] = newValue } } 22 mutating func insert(_ product: Product) { var productsInCategory = self[product.category] productsInCategory.append(product) self[product.category] = productsInCategory }
23. COLLECTIONSUNDERHOOD Some sugar for clean code ▸ CustomStringConvertible ▸ CustomDebugStringConvertible ▸ CustomReflectable 23
24. COLLECTIONSUNDERHOOD class MyClass { let value1: Int = 1 let value2: Int = 2 } let myClass = MyClass() print(myClass) (lldb) po myClass Demo.MyClass <MyClass: 0x6000023eeda0> 24
25. COLLECTIONSUNDERHOOD protocol CustomStringConvertible { var description: String { get } } protocol CustomDebugStringConvertible { var debugDescription: String { get } } 25
26. COLLECTIONSUNDERHOOD extension MyClass: CustomStringConvertible { var description: String { return "\(value1) & \(value2)" } } extension MyClass: CustomDebugStringConvertible { var debugDescription: String { return "debug \(value1) & \(value2)" } } 26
27. COLLECTIONSUNDERHOOD print(myClass) (lldb) po myClass 1 & 2 debug 1 & 2 27
28. COLLECTIONSUNDERHOOD let str = String(describing: myClass) let debugStr = String(reflecting: myClass) 28
29. COLLECTIONSUNDERHOOD let myClasses = [myClass1, myClass2, myClass3] ▿ 3 elements ▿ 0 : debug 1 & 2 ▿ 1 : debug 1 & 2 ▿ 2 : debug 1 & 2 29 [debug 1 & 2, debug 1 & 2, debug 1 & 2] print(myClasses) (lldb) po myClasses
30. COLLECTIONSUNDERHOOD 30 func _makeCollectionDescription( withTypeName type: String? = nil ) -> String { ... }
31. COLLECTIONSUNDERHOOD 31 var result = "" if let type = type { result += "\(type)([" } else { result += "[" }
32. COLLECTIONSUNDERHOOD var first = true for item in self { if first { first = false } else { result += ", " } debugPrint(item, terminator: "", to: &result) } 32
33. COLLECTIONSUNDERHOOD 33 result += type != nil ? "])" : "]" return result
34. COLLECTIONSUNDERHOOD Mirror 34 ▸ Introspection ▸ Reflection ▸ CustomReflectable
35. COLLECTIONSUNDERHOOD CustomReflectable 35 protocol CustomReflectable { public var customMirror: Mirror { get } }
36. COLLECTIONSUNDERHOOD 36 func reset() { let mirror = Mirror(reflecting: self) for child in mirror.children { if let purgeable = child.value as? Purgeable { purgeable.purge() } } }
37. COLLECTIONSUNDERHOOD Encodable Decodable Equatable Hashable 37
38. DICTIONARY SET ARRAY(?) 38
39. COLLECTIONSUNDERHOOD Dictionary ▸ ExpressibleByDictionaryLiteral 39
40. COLLECTIONSUNDERHOOD Dictionary 40 Sequence Dictionary Collection Equatable Decodable Encodable Hashable CustomDebugStringConvertible CustomReflectable CustomStringConvertible ExpressibleByDictionaryLiteral
41. COLLECTIONSUNDERHOOD Dictionary ▸ ExpressibleByDictionaryLiteral ▸ _HashTable ▸ Two storage schemes ▸ Native ▸ Cocoa 41
42. COLLECTIONSUNDERHOOD Native Storage class __RawDictionaryStorage <isa> <refcount> _count _capacity _scale _age _seed _rawKeys _rawValue [inline bitset of occupied entries] [inline array of keys] [inline array of values] struct Dictionary<K, V> enum Dictionary<K, V>._Variant struct _NativeDictionary<K, V> 42
43. COLLECTIONSUNDERHOOD Cocoa Storage class NSDictionary [refcount] … struct __CocoaDictionary.Index allKeys currentKeyIndex struct Dictionary<K, V> enum Dictionary<K, V>._Variant struct __CocoaDictionary 43
44. COLLECTIONSUNDERHOOD Big O notation ▸ NSDictionary to Dictionary<NSObject, AnyObject> — O(1) ▸ NSDictionary to Dictionary<AnyHashable, AnyObject> — O(n) ▸ Dictionary<K, V> to NSDictionary — O(1) 44
45. COLLECTIONSUNDERHOOD Set ▸ Two storage schemes ▸ Native ▸ Cocoa ▸ _HashTable ▸ ExpressibleByArrayLiteral ▸ SetAlgebra 45
46. COLLECTIONSUNDERHOOD Set 46 Sequence Set Collection Equatable Decodable Encodable Hashable CustomDebugStringConvertible CustomReflectable CustomStringConvertible ExpressibleByArrayLiteral SetAlgebra
47. COLLECTIONSUNDERHOOD mutating func formIntersection(_:) mutating func formSymmetricDifference(_:) mutating func formUnion(_:) mutating func subtract(_:) func intersection(_:) func subtracting(_:) func symmetricDifference(_:) func union(_:) ... SetAlgebra 47
48. COLLECTIONSUNDERHOOD ArrayType ▸ Array ▸ ArraySlice ▸ ContiguousArray 48
49. COLLECTIONSUNDERHOOD ArrayType 49 ExpressibleByArrayLiteral Sequence Array Collection Equatable Decodable Encodable Hashable CustomDebugStringConvertible CustomReflectable CustomStringConvertible RandomAccessCollection BidirectionalCollection RangeReplaceableCollection MutableCollection
50. A collection that supports backward as well as forward traversal. Apple’s Doc COLLECTIONSUNDERHOOD BidirectionalCollection 50
51. COLLECTIONSUNDERHOOD func index(before i: Index) -> Index func formIndex(before i: inout Index) mutating func removeLast(_ k: Int) mutating func removeLast() -> Element mutating func popLast() -> Element? ... BidirectionalCollection 51
52. COLLECTIONSUNDERHOOD mutating func removeLast() -> Element { let element = last! self = self[startIndex..<index(before: endIndex)] return element } BidirectionalCollection 52
53. COLLECTIONSUNDERHOOD RandomAccessCollection 53 ▸ Inherited from BidirectionalCollection ▸ O(1) ▸ where Index: Strideable
54. COLLECTIONSUNDERHOOD Mutating & Replacing 54 ▸ MutableCollection ▸ RangeReplaceableCollection
55. COLLECTIONSUNDERHOOD MutableCollection 55 ▸ Save length ▸ Save order
56. COLLECTIONSUNDERHOOD RangeReplaceableCollection 56 ▸ Save length ▸ Save order ▸ Bad semantic
57. COLLECTIONSUNDERHOOD ContiguousArray 57
58. COLLECTIONSUNDERHOOD (Simple)Array 58
59. COLLECTIONSUNDERHOOD ArraySlice 59
60. COLLECTIONSUNDERHOOD typealias A = ArraySlice<Bool> func sieveOfEratosthenes(limit: Int) -> [Int] { var possibles = A(repeating: true, count: limit + 1) var result = [Int]() for i in 2 ... limit { guard possibles[i] else { continue } for j in stride(from: i * i, through: limit, by: i) { possibles[j] = false } result.append(i) } return result } 60
61. COLLECTIONSUNDERHOOD 61 t, s 1,65 3,3 4,95 6,6 Array ArraySlice ContiguousArray 3,24 3,31 6,51
62. OBJECTIVE-С HERITAGE 62
63. COLLECTIONSUNDERHOOD Objective-С Heritage 63 ▸ NSPointerArray ▸ NSMapTable ▸ NSHashTable
64. COLLECTIONSUNDERHOOD Conclusion 64 ▸ Collections > 5 ▸ Use Swift’s protocols ▸ Dictionary, Set, ArrayType ▸ Array is slow ▸ NSPointerArray, NSMapTable, NSHashTable
65. REFERENCES 65
66. COLLECTIONSUNDERHOOD 66 ▸ https://www.swiftbysundell.com/posts/creating-custom-collections-in-swift ▸ https://yandexdataschool.ru/edu-process/courses/algorithms#item-6 ▸ https://github.com/apple/swift/blob/ 6fc4cef671947d1d2482951853f7f82854473d91/docs/Arrays.rst ▸ https://marcosantadev.com/swift-arrays-holding-elements-weak-references
67. CONTACTS 67 medium.com/@Georguy @eigeorguy