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A tiny realization of a reactive approach.
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| import PlaygroundSupport | |
| import Foundation | |
| class WeakRef<T> where T: AnyObject { | |
| private(set) weak var value: T? | |
| init(value: T?) { | |
| self.value = value | |
| } | |
| } | |
| class Observer<Element> { | |
| private let on: (Element) -> Void | |
| init(_ on: @escaping (Element) -> Void) { | |
| self.on = on | |
| } | |
| func on(_ event: Element) { | |
| on(event) | |
| } | |
| } | |
| class Observable<Element> { | |
| typealias WeakObserver = WeakRef<Observer<Element>> | |
| private var observers: [WeakObserver] = [] | |
| private let isolationQueue = DispatchQueue(label: "", attributes: .concurrent) | |
| private var _value: Element | |
| var value: Element { | |
| get { | |
| isolationQueue.sync { _value } | |
| } | |
| set { | |
| isolationQueue.async(flags: .barrier) { | |
| self._value = newValue | |
| self.observers.forEach { $0.value?.on(newValue) } | |
| } | |
| } | |
| } | |
| private var transform: ((Element) -> Element)? | |
| init(value: Element) { | |
| self._value = value | |
| } | |
| func subscribe(onNext: @escaping (Element) -> Void) -> Observer<Element> { | |
| let transform = self.transform ?? { $0 } | |
| let observer = Observer<Element> { element in | |
| onNext(transform(element)) | |
| } | |
| observers.append(.init(value: observer)) | |
| return observer | |
| } | |
| func map(_ transform: @escaping (Element) -> Element) -> Observable<Element> { | |
| self.transform = transform | |
| return self | |
| } | |
| } | |
| let observable = Observable<Int>(value: 0) | |
| let observer = observable | |
| .map { $0 + 1 } | |
| .subscribe { print($0) } | |
| for i in 1...5 { | |
| observable.value = i | |
| } | |
| // 2, 3, 4, 5, 6 | |
| PlaygroundPage.current.needsIndefiniteExecution = true |
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