JuniorTheoryCommon

What does the program print?

SWIFT

func makeCounter() -> () -> Int {
    var count = 0
    return {
        count += 1
        return count
    }
}

let c1 = makeCounter()
let c2 = c1
print(c1(), c2(), c1())

1 2 3

Expecting 1 1 2: thinking let c2 = c1 copies the closure as it would copy an array. Both names lead to one closure, so they share one count.
Expecting 1 1 1: thinking var count = 0 runs on every call. It runs once, when makeCounter is called, and the closure keeps that variable.

What does the program print if c2 is a second makeCounter() call instead?
Why may the closure change count even though c1 is a let constant?

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JuniorTheoryCommon

What does the program print?

SWIFT

func makeCounter() -> () -> Int {
    var count = 0
    return {
        count += 1
        return count
    }
}

let c1 = makeCounter()
let c2 = c1
print(c1(), c2(), c1())

1 2 3

Expecting 1 1 2: thinking let c2 = c1 copies the closure as it would copy an array. Both names lead to one closure, so they share one count.
Expecting 1 1 1: thinking var count = 0 runs on every call. It runs once, when makeCounter is called, and the closure keeps that variable.

What does the program print if c2 is a second makeCounter() call instead?
Why may the closure change count even though c1 is a let constant?

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