How do you drive an animation per frame with CADisplayLink, and why does it leak its target?

Predict first

Does the owner die when the last reference goes, with a plain target and with a weak proxy?

import UIKit

final class Ticker: NSObject {
    var link: CADisplayLink?; var n = 0
    deinit { print("Ticker deinit") }
    @objc func tick(_ l: CADisplayLink) { n += 1 }
}
final class Proxy { weak var target: Ticker?; init(_ t: Ticker) { target = t }; @objc func tick(_ l: CADisplayLink) { target?.tick(l) } }

var t: Ticker? = Ticker(); weak var w = t
t!.link = CADisplayLink(target: t!, selector: #selector(Ticker.tick(_:)))
t!.link!.add(to: .main, forMode: .common)
RunLoop.main.run(until: Date().addingTimeInterval(0.5))
print("ticking:", t!.n > 0)
let link = t!.link!
t = nil
print("released, alive:", w != nil)
link.invalidate()
print("invalidated, alive:", w != nil)

var t2: Ticker? = Ticker(); weak var w2 = t2
let proxy = Proxy(t2!)
let dl = CADisplayLink(target: proxy, selector: #selector(Proxy.tick(_:))); dl.add(to: .main, forMode: .common)
t2 = nil
print("proxy, alive:", w2 != nil)
dl.invalidate()

• ticking: true, released, alive: true, Ticker deinit, invalidated, alive: false, Ticker deinit, proxy, alive: false
• ticking: true, released, alive: false, Ticker deinit, invalidated, alive: false, Ticker deinit, proxy, alive: false
• ticking: false, released, alive: true, Ticker deinit, invalidated, alive: false, proxy, alive: true