JuniorTheoryCommon

What does the program print (lines separated by spaces)?

SWIFT

class Screen {
    var onTap: () -> Void = {}
    init() {
        onTap = { [weak self] in print(self == nil) }
    }
    deinit { print("bye") }
}

var screen: Screen? = Screen()
let tap = screen!.onTap
screen = nil
tap()

bye true

Expecting false: thinking the stored closure keeps the screen alive. [weak self] adds nothing to the count, so screen = nil frees the object and deinit prints bye.
Expecting a crash: mixing up [weak self] with [unowned self]. A weak self of a freed object is nil, and the closure runs safely.

What changes if the closure uses self without a capture list?
Why does Swift require self. to be written explicitly in such a closure?

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JuniorTheoryCommon

What does the program print (lines separated by spaces)?

SWIFT

class Screen {
    var onTap: () -> Void = {}
    init() {
        onTap = { [weak self] in print(self == nil) }
    }
    deinit { print("bye") }
}

var screen: Screen? = Screen()
let tap = screen!.onTap
screen = nil
tap()

bye true

Expecting false: thinking the stored closure keeps the screen alive. [weak self] adds nothing to the count, so screen = nil frees the object and deinit prints bye.
Expecting a crash: mixing up [weak self] with [unowned self]. A weak self of a freed object is nil, and the closure runs safely.

What changes if the closure uses self without a capture list?
Why does Swift require self. to be written explicitly in such a closure?

Back to questions Open topic in roadmap →Answer it yourself — Quiz