final class WeakStrongButton {
    private weak var weakItem: AnyObject?
    private var eventClosure: (() -> Void)?

    func fireEvent() {
        guard let eventClosure = eventClosure else { return }
        eventClosure()
    }
    func onEvent<T: AnyObject>(weakly object: T, closure: @escaping (T) -> Void) {
        eventClosure = { [weak object] in
            guard let object = object else { return }
            closure(object)
        }
    }
}

final class Foo {
    let button = WeakStrongButton()

    init() {
        button.onEvent(weakly: self) { foo in
            print(foo)
        }
    }
    deinit { print("deinit") }
    func fire() {
        button.fireEvent()
    }
}

do {
    let foo = Foo()
    foo.fire()
}