Question

How to use higher-order functions in Swift

Answer 1

// A higher‑order function is a function that does at least one of the following:
// 1. Takes another function as an argument
// 2. Returns a function as its result
// If it does either one, it qualifies.

// Higher-order function: takes a function as an argument
func applyTwice(_ fn: (Int) -> Int, _ x: Int) -> Int {
    return fn(fn(x))
}

// A simple function to pass in
func add3(_ n: Int) -> Int {
    return n + 3
}

// Use the higher-order function
let result = applyTwice(add3, 5) // 5 + 3 = 8 + 3 = 11

print(result)



/*
run:

11

*/

 

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Answer 2

// A higher‑order function is a function that does at least one of the following:
// 1. Takes another function as an argument
// 2. Returns a function as its result
// If it does either one, it qualifies.

// makeMultiplier is a higher‑order function because it RETURNS another function
func makeMultiplier(_ n: Int) -> (Int) -> Int {

    // This inner function forms a closure and remembers the value of n
    return { x in
        return x * n // Uses the captured value n
    }
}

// double_val is now a function created by makeMultiplier(2)
// It remembers n = 2 through closure
let double_val = makeMultiplier(2)

// Calling double_val(10) multiplies 10 by the captured n (which is 2)
print(double_val(10))



/*
run:

20

*/

 

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