Crash when mutating [UIColor] in a struct on a UIView prior to adding that view as a UIViewController's subview

CrashViewController.swift

import UIKit

/**
 This code *consistently* crashes when built with
 the following Xcode 10.2.1 build settings:

 `Swift Version` = `5` (i.e. default)
 `Enable Testability` = `NO`
 `Optimization Level` = `-Owholemodule`

 Download the Xcode project zip here:
 http://bit.ly/2JDPb6b
*/

struct ViewModel {
    var colors: [UIColor]

    init(colors: [UIColor]) {
        self.colors = colors
    }
}

class CrashView: UIView {
    var colors: [UIColor] = []

    var model: ViewModel {
        didSet { self.colors = model.colors }
    }

    init() {
        self.model = ViewModel(colors: [UIColor.black, UIColor.gray])
        super.init(frame: .zero)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func layoutSubviews() {
        super.layoutSubviews()

        // 2:
        accessColors()
    }

    func accessColors() {
        // 3:
        print(model.colors)
    }
}

class ViewController: UIViewController {
    let crashView = CrashView()

    override func viewDidLoad() {
        super.viewDidLoad()

        // 1:
        crashView.model.colors = [UIColor.blue, UIColor.green]
        view.addSubview(crashView)
    }
}

Here is a more minimum repro that doesn’t require views or VCs at all:

struct Stage {
    var backupDancers: [Any] = []
}

class Performance {
    var stage: Stage? = Stage()
    
    func andDaaaaaance() {
        print(stage?.backupDancers.count) // crashes
    }
}

class DanceHall {
    let performance = Performance()
    
    func letsParty() {
        setTheStage()
        performance.andDaaaaaance()
    }
    
    func setTheStage() {
        let randomPerson = NSObject()
        performance.stage?.backupDancers = [randomPerson]
    }
}

Here is a **more** minimum repro that doesn’t require views or VCs at all: ``` struct Stage { var backupDancers: [Any] = [] } class Performance { var stage: Stage? = Stage() func andDaaaaaance() { print(stage?.backupDancers.count) // crashes } } class DanceHall { let performance = Performance() func letsParty() { setTheStage() performance.andDaaaaaance() } func setTheStage() { let randomPerson = NSObject() performance.stage?.backupDancers = [randomPerson] } } ```

…

On Mon, Sep 2, 2019 at 1:05 AM Marcin Krzyzanowski ***@***.***> wrote: what’s the stacktrace. shiuldnt you override loadView and instantiate ‘self.view = UIView()’ first? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <https://gist.github.com/51a40d6e2771d9229dcc629512200202?email_source=notifications&email_token=ABHCY566J7IBB7ZMS4KPQ7DQHTCMVA5CNFSM4IS2XLJ2YY3PNVWWK3TUL52HS4DFVNDWS43UINXW23LFNZ2KUY3PNVWWK3TUL5UWJTQAFX7JW#gistcomment-3014299>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABHCY56BYM4GIGJFAQE56XDQHTCMVANCNFSM4IS2XLJQ> .