Swift Combine's Publisher for CADisplayLink

CADisplayLink+Combine.swift

import Combine
import QuartzCore.CADisplayLink

extension CADisplayLink {
    fileprivate class DisplayLinkWrapper {
        private var subscriber: AnySubscriber<CADisplayLink, Never>
        private var displayLink: CADisplayLink?

        init(runloop: RunLoop, mode: RunLoop.Mode, subscriber: AnySubscriber<CADisplayLink, Never>) {
            self.subscriber = subscriber
            self.displayLink = CADisplayLink(target: self, selector: #selector(displayLinkHandler))
            self.displayLink?.add(to: runloop, forMode: mode)
        }

        @objc func displayLinkHandler(displayLink: CADisplayLink) {
            _ = subscriber.receive(displayLink)
        }

        deinit {
            displayLink?.invalidate()
        }
    }

    static func publisher(to runloop: RunLoop, forMode mode: RunLoop.Mode) -> AnyPublisher<CADisplayLink, Never> {
        return Publishers.Deferred<AnyPublisher<CADisplayLink, Never>> {
            var displayLinkWrapper: DisplayLinkWrapper?
            return AnyPublisher { subscriber in
                displayLinkWrapper = DisplayLinkWrapper(runloop: runloop, mode: mode, subscriber: subscriber)
                }
                .handleEvents(receiveCancel: {
                    if displayLinkWrapper != nil {
                        displayLinkWrapper = nil
                    }
                }).eraseToAnyPublisher()
            }.eraseToAnyPublisher()
    }
}