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//
// ObserverList.swift
// MullvadVPN
//
// Created by pronebird on 26/06/2020.
// Copyright © 2020 Mullvad VPN AB. All rights reserved.
//
import Foundation
struct WeakBox<T> {
var value: T? {
return valueProvider()
}
private let valueProvider: () -> T?
init(_ value: T) {
let reference = value as AnyObject
valueProvider = { [weak reference] in
return reference as? T
}
}
static func == (lhs: WeakBox<T>, rhs: T) -> Bool {
return (lhs.value as AnyObject) === (rhs as AnyObject)
}
}
final class ObserverList<T> {
private let lock = NSLock()
private var observers = [WeakBox<T>]()
func append(_ observer: T) {
lock.lock()
let hasObserver = observers.contains { box in
return box == observer
}
if !hasObserver {
observers.append(WeakBox(observer))
}
lock.unlock()
}
func remove(_ observer: T) {
lock.lock()
let index = observers.firstIndex { box in
return box == observer
}
if let index = index {
observers.remove(at: index)
}
lock.unlock()
}
func forEach(_ body: (T) -> Void) {
lock.lock()
var indicesToRemove = [Int]()
var observersToNotify = [T]()
for (index, box) in observers.enumerated() {
if let observer = box.value {
observersToNotify.append(observer)
} else {
indicesToRemove.append(index)
}
}
for index in indicesToRemove.reversed() {
observers.remove(at: index)
}
lock.unlock()
for observer in observersToNotify {
body(observer)
}
}
}
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