Tricky output-based questions on Closures — Part III

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

let counter = makeCounter()
print(counter())
print(counter())

Output Explanation:

• The makeCounter function returns a closure that increments and returns a counter value.
• The defer statement defers the execution of the count += 1 statement until the end of the closure's scope.
• So, when counter is called twice, it first returns 0 and then 1.
• So, the output will be: 0, 1.

func repeatClosure(_ closure: () -> Void, times: Int) {
    for _ in 0..<times {
        closure()
    }
}

var counter = 0
let incrementCounter = { counter += 1 }

repeatClosure(incrementCounter, times: 3)
print(counter)

Output Explanation:

• The repeatClosure function repeats the given closure times number of times.
• Inside the closure, the counter variable is incremented by 1.
• After calling repeatClosure with incrementCounter as the closure and repeating it 3 times, the value of counter will be 3.
• So, the output will be: 3.

func generateClosures() -> [() -> Int] {
    var closures: [() -> Int] = []
    for i in 1...3 {
        closures.append { i }
    }
    return closures
}

let closures = generateClosures()
let results = closures.map { $0() }
print(results)

Output Explanation:

• This code snippet creates an array of closures that each return the current value of i.
• However, since i is captured by reference in the closures, they all share the same value.
• At the time the closures are executed (when map is called), the value of i will be 4 because it's the value that completes the loop.
• So, the output will be: [4, 4, 4].

func performOperation(_ operation: () -> Void) {
    print("Before operation")
    operation()
    print("After operation")
}

func createClosure(_ value: Int) -> () -> Void {
    return {
        print(value)
    }
}

let closure1 = createClosure(10)
let closure2 = createClosure(20)

performOperation(closure1)
performOperation(closure2)

Output Explanation:

• The createClosure function returns a closure that captures and prints the value parameter.
• When closure1 is executed inside performOperation, it prints the captured value of value, which is 10.
• Similarly, when closure2 is executed inside performOperation, it prints the captured value of value, which is 20.
• So, the output will be:

Before operation
10
After operation
Before operation
20
After operation

var result = 0
let closure1 = { result += 10 }
let closure2 = { [result] in print(result) }

closure1()
closure2()

Output Explanation:

• closure1 modifies the result variable directly.
• closure2 captures result as a constant at the time of its creation.
• When closure1 is called, it modifies result to 10.
• When closure2 is called, it prints the captured value of result, which is 0 because it was captured before closure1 executed.
• So, the output will be: 0.