CODEWITHSUNDEEP
swiftclosures
Cristian Lăpușan
Cristian Lăpușan

Reputation: 9

capturing values in Swift

I do not understand how capturing values works. Below an example of a nested function that captures amount and runningTotal from its surrounding function. when calling makeIncrementer(forIncrement:) function, nothing happens inside incrementer() function (the code inside incrementer() function doesn’t get executed), so how can incrementer() capture any value? I’m obviously a novice in programming and I couldn’t find a detailed explanation of what is actually going on “under the hood”.

func makeIncrementer(forIncrement amount: Int) -> () -> Int {
    var runningTotal = 0
    func incrementer() -> Int {
        runningTotal += amount
        return runningTotal
    }
    return incremented
}

let incrementByTen = makeIncrementer(forIncrement: 10)
incrementByTen()
// returns a value of 10
incrementByTen()
// returns a value of 20
incrementByTen()
// returns a value of 30

Upvotes: 1

Views: 339

Answers (1)

newacct
newacct

Reputation: 122439

That's how closures work -- they capture variables from the surrounding scope when they are created.

Upvotes: 0

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