11 Most Asked Swift Programming Questions

Swift 5 provides a method called enumerated() for Array. enumerated() has the following declaration:

func enumerated() -> EnumeratedSequence<Array<Element>>

Returns a sequence of pairs (n, x), where n represents a consecutive integer starting at zero and x represents an element of the sequence.

In the simplest cases, you may use enumerated() with a for loop. For example:

let list = ["Car", "Bike", "Plane", "Boat"]
for (index, element) in list.enumerated() {
    print(index, ":", element)
}

/*
prints:
0 : Car
1 : Bike
2 : Plane
3 : Boat
*/

Note: However that you’re not limited to use enumerated() with a for loop. In fact, if you plan to use enumerated() with a for loop for something similar to the following code, you’re doing it wrong:

let list = [Int](1...5)
var arrayOfTuples = [(Int, Int)]()

for (index, element) in list.enumerated() {
    arrayOfTuples += [(index, element)]
}

print(arrayOfTuples) // prints [(0, 1), (1, 2), (2, 3), (3, 4), (4, 5)]

A swiftier way to do this is:

let list = [Int](1...5)
let arrayOfTuples = Array(list.enumerated())
print(arrayOfTuples) // prints [(offset: 0, element: 1), (offset: 1, element: 2), (offset: 2, element: 3), (offset: 3, element: 4), (offset: 4, element: 5)]

As an alternative, you may also use enumerated() with map:

let list = [Int](1...5)
let arrayOfDictionaries = list.enumerated().map { (a, b) in return [a : b] }
print(arrayOfDictionaries) // prints [[0: 1], [1: 2], [2: 3], [3: 4], [4: 5]]

Moreover, although it has some limitations, forEach can be a good replacement to a for loop:

let list = [Int](1...5)
list.reversed().enumerated().forEach { print($0, ":", $1) }

/*
prints:
0 : 5
1 : 4
2 : 3
3 : 2
4 : 1
*/

By using enumerated() and makeIterator(), you can even iterate manually on your Array. For example:

import UIKit
import PlaygroundSupport

class ViewController: UIViewController {

    var generator = ["Car", "Bike", "Plane", "Boat"].enumerated().makeIterator()

    override func viewDidLoad() {
        super.viewDidLoad()

        let button = UIButton(type: .system)
        button.setTitle("Tap", for: .normal)
        button.frame = CGRect(x: 100, y: 100, width: 100, height: 100)
        button.addTarget(self, action: #selector(iterate(_:)), for: .touchUpInside)
        view.addSubview(button)
    }

    @objc func iterate(_ sender: UIButton) {
        let tuple = generator.next()
        print(String(describing: tuple))
    }

}

PlaygroundPage.current.liveView = ViewController()

/*
 Optional((offset: 0, element: "Car"))
 Optional((offset: 1, element: "Bike"))
 Optional((offset: 2, element: "Plane"))
 Optional((offset: 3, element: "Boat"))
 nil
 nil
 nil
 */

5. Is there a replacement/solution for #ifdef where you can define a macro using compiler preprocessors?

Answer:

#if DEBUG
    let a = 2
#else
    let a = 3
#endif

It works, but it doesn’t seem to be recognized in a playground though.

Important Note: -DDEBUG=1 doesn’t work. Only -D DEBUG works. Seems compiler is ignoring a flag with a specific value.