All func pointers need a protocol now?

Question

Gargoyle OP

Created Dec ’15

Replies 6

Boosts 0

Views 1.3k

Participants 2

I'm trying to do this simple callback method:

 final class MyView: UIView {
    var onSomeAction: ((String) -> Void)!
}
 
final class MyViewController: UIViewController {
    let myView = MyView(frame: CGRectZero)
    override func viewDidLoad() {
        super.viewDidLoad()
        myView.onSomeAction = someFunc
    }
 
    private func someFunc(str: String) {
    }
}

But that's going to create a retain cycle (I believe). I can't just mark the onSomeAction var as weak because that's a compile time error.

Do I really need to go to the level of defining a protocol for this just so I can mark it as a class protocol and then mark that callback to be a weak reference?

I've gotta be missing something here.

Answered by Jessy in 98724022

 var onSomeAction_get: () -> (String -> Void)! = {nil}
 
myView.onSomeAction_get = {[unowned self] in self.someFunc}

Boost

Answer 1

Jessy OP

Dec ’15

Accepted Answer

 var onSomeAction_get: () -> (String -> Void)! = {nil}
 
myView.onSomeAction_get = {[unowned self] in self.someFunc}

0

Answer 2

Gargoyle OP

Dec ’15

That doesn't really make sense. You're still capturing a strong reference in MyView. Your [unowned self] just says that the closure itself won't capture itself strongly.

0

Answer 3

Jessy OP

Dec ’15

Fixed. Sorry. Tired.

This is one of my use cases for mutable property accessors.

0

Answer 4

Jessy OP

Jan ’16

So, what's your take? This is what I've been using as a replacement for delegates, except with weak instead of unowned.

0

Answer 5

Gargoyle OP

Jan ’16

It definitely has to be weak, and I think it would work. Just feels a bit like a missing language feature. It's too easy to just assign a function to a property like this and think things are OK, only to later realize you've made a retain cycle. We should somehow be able to tell Swift that the pointer to the closure should always be weak without needing a protocol for it.

0

Answer 6

Jessy OP

Jan ’16

I agree.

And as for mutable accessors, here's what I use when both get and set need to be mutable:

https://github.com/Catterwaul/HemiprocneMystacea/blob/master/HemiprocneMystacea/Swift/Properties/Mutable%20Properties.swift

What I want this to look like is this:

 weak var onSomeAction: (String -> Void)?
myView.onSomeAction get = {[weak self] in self?.someFunc}

0

	final class MyView: UIView {
	var onSomeAction: ((String) -> Void)!
	}

	final class MyViewController: UIViewController {
	let myView = MyView(frame: CGRectZero)
	override func viewDidLoad() {
	super.viewDidLoad()
	myView.onSomeAction = someFunc
	}

	private func someFunc(str: String) {
	}
	}

	var onSomeAction_get: () -> (String -> Void)! = {nil}

	myView.onSomeAction_get = {[unowned self] in self.someFunc}

	weak var onSomeAction: (String -> Void)?
	myView.onSomeAction get = {[weak self] in self?.someFunc}