Dangers of implicitly unwrapped optionals

IUO.swift

//: Playground - noun: a place where people can play

import UIKit
import PlaygroundSupport

class ViewController: UIViewController {
    lazy var tapHandler: TapHandler = TapHandler(delegate: self, view: self.view)
}

extension ViewController: TapHandlerDelegate {
    func handleTap() {
    }
}

protocol TapHandlerDelegate: class {
    func handleTap()
}

class TapHandler {
    weak var delegate: TapHandlerDelegate!

    init() {
    }

    init(delegate: TapHandlerDelegate, view: UIView) {
        self.delegate = delegate
        let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(tapReceived))
        view.addGestureRecognizer(tapGestureRecognizer)
    }

    @objc func tapReceived() {
        self.delegate.handleTap()
    }
}

var tapHandler = TapHandler()
autoreleasepool {
    let viewController = ViewController()
    tapHandler = viewController.tapHandler
    print(tapHandler.delegate) //prints the viewController
}
print(tapHandler)
print(tapHandler.delegate) // crashes

Yep, this shows the problem.

You could also change the last line to tapHandler.handleTap() which would make it more 'real world'