Property Wrappers の特徴を眺める #swiftzoomin
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2020/03/21 に swift zoomin' で発表した資料です。プロパティーアクセスしたときに追加処理を行う仕組みの Property Wrappers を、類似機能に感じる didSet と、同じく似たようなことが実現できうる独自型について、特徴を比較しながら Property Wrappers とはどういったものなのかを眺めていきます。
![@propertyWrapper
struct Sorting<Element:Comparable> {
private var elements: [Element]
init(wrappedValue: [Element]) {
elements = wrappedValue
}
var wrappedValue: [Element] {
get { elements }
set { elements = newValue.sorted() }
}
}
@Sorting var values: [Int] = []](https://image.slidesharecdn.com/swiftzoominpropertywrappers-200321134357/85/Property-Wrappers-swiftzoomin-10-320.jpg)
![var values: [Int] = [] {
didSet {
values = values.sorted()
}
}](https://image.slidesharecdn.com/swiftzoominpropertywrappers-200321134357/85/Property-Wrappers-swiftzoomin-11-320.jpg)
![struct OrderedArray<Element : Comparable> {
private(set) var elements: [Element]
public init() {
elements = []
}
mutating
func append(_ element: Element) {
elements =
(elements + [element]).sorted()
}
}
var values: OrderedArray<Int>](https://image.slidesharecdn.com/swiftzoominpropertywrappers-200321134357/85/Property-Wrappers-swiftzoomin-12-320.jpg)
![_
A Type
@Sorting var values: [Int]
private
var _values: Sorting<Int>](https://image.slidesharecdn.com/swiftzoominpropertywrappers-200321134357/85/Property-Wrappers-swiftzoomin-23-320.jpg)
![@propertyWrapper
extension Sorting {
func ascending -> [Element] {
elements.sorted(by: <)
}
}
A Type
@Sorting var values: [Int]
func XXXX() {
_values.sorted(by: .ascending)](https://image.slidesharecdn.com/swiftzoominpropertywrappers-200321134357/85/Property-Wrappers-swiftzoomin-24-320.jpg)
![@propertyWrapper
struct Sorting<Element> {
init(wrappedValue: [Element], order: Order) {
}
A Type
@Sorting(order: .descending) var values: [Int] = []](https://image.slidesharecdn.com/swiftzoominpropertywrappers-200321134357/85/Property-Wrappers-swiftzoomin-25-320.jpg)
![@propertyWrapper
struct Sorting<Element> {
init() {
elements = []
}
A Type
@Sorting var values: [Int]](https://image.slidesharecdn.com/swiftzoominpropertywrappers-200321134357/85/Property-Wrappers-swiftzoomin-26-320.jpg)
![$
A Type
@Sorting var values: [Int]
private
var $values: SomeType
@propertyWrapper
struct Sorting<Element> {
var projectedValue: SomeType {
}](https://image.slidesharecdn.com/swiftzoominpropertywrappers-200321134357/85/Property-Wrappers-swiftzoomin-27-320.jpg)
Property Wrappers の特徴を眺める #swiftzoomin
- 5. @propertyWrapper wrappedValue @propertyWrapper struct PassThrough<Value> { var wrappedValue: Value init(wrappedValue value: Value) { wrappedValue = value } }
- 6. @型名 wrappedValue struct Data { @PassThrough var value: Int }
- 7. Object @XXX var value: YYY @propertyWrapper XXX init(wrappedValue:) var wrappedValue
- 10. @propertyWrapper struct Sorting<Element:Comparable> { private var elements: [Element] init(wrappedValue: [Element]) { elements = wrappedValue } var wrappedValue: [Element] { get { elements } set { elements = newValue.sorted() } } } @Sorting var values: [Int] = []
- 11. var values: [Int] = [] { didSet { values = values.sorted() } }
- 12. struct OrderedArray<Element : Comparable> { private(set) var elements: [Element] public init() { elements = [] } mutating func append(_ element: Element) { elements = (elements + [element]).sorted() } } var values: OrderedArray<Int>
- 21. > > defer
- 23. _ A Type @Sorting var values: [Int] private var _values: Sorting<Int>
- 24. @propertyWrapper extension Sorting { func ascending -> [Element] { elements.sorted(by: <) } } A Type @Sorting var values: [Int] func XXXX() { _values.sorted(by: .ascending)
- 25. @propertyWrapper struct Sorting<Element> { init(wrappedValue: [Element], order: Order) { } A Type @Sorting(order: .descending) var values: [Int] = []
- 26. @propertyWrapper struct Sorting<Element> { init() { elements = [] } A Type @Sorting var values: [Int]
- 27. $ A Type @Sorting var values: [Int] private var $values: SomeType @propertyWrapper struct Sorting<Element> { var projectedValue: SomeType { }