WeakList.swift

class WeakList<T: AnyObject> {
    private class WeakRef {
        private(set) weak var value: T?
        
        init(_ value: T) {
            self.value = value
        }
    }
    
    private var arr = [WeakRef]()
    
    var count: Int {
        arr = arr.filter { $0.value != nil }
        return arr.count
    }
    
    var allObjects: [T] {
        let values = arr.map { $0.value }
        return values.compactMap { $0 }
    }
    
    var lastObject: T? {
        for i in (0..<arr.count).reversed() {
            if let object = arr[i].value {
                return object
            } else {
                arr.remove(at: i)
            }
        }
        return nil
    }
    
    func addObject(_ object: T) {
        arr.append(WeakRef(object))
    }
    
    func removeObject(_ object: T) -> Int? {
        for i in 0..<arr.count {
            if let item = arr[i].value {
                if item === object {
                    arr.remove(at: i)
                    return i
                }
            } else {
                arr.remove(at: i)
            }
        }
        return nil
    }
    
    func removeLast() {
        for i in (0..<arr.count).reversed() {
            if arr.remove(at: i).value != nil {
                return
            }
        }
    }
    
    func removeAllObjects() {
        arr.removeAll()
    }
}