Weak.swift

import Foundation

class Weak<T> {
  private weak var _value: AnyObject?
  var value: T? { return _value as? T }
  
  init(_ value: T) {
    _value = value as AnyObject
  }
}

extension Array {
  mutating func cleanup<T>() where Element == Weak<T> {
    self = self.filter { $0.value != nil }
  }
}