How to create 15 digit length random string in Swift?

Question

In Javascript, Node.js I can generate with https://www.npmjs.com/package/uuid package a 15 digit length "random" string. Is it possible it with Swift?

Like this: 802128100247740

const uuidv4 = require("uuid/v4");
tempUserUuid = uuidv4();

Answer 1

Swift 5.0 introduced major improvements in dealing with random values and elements. The following code will help you

func randomString(length: Int) -> String {
  let letters = "0123456789"
  return String((0..<length).map{ _ in letters.randomElement()! })
}

label.text = randomString(length: 15)

Answer 2

The other answers generate a random number multiple times, but you only need to do it once.

import Foundation

extension String {
  /// A leading-zero-padded padded random number.
  /// - Returns: nil if digitCount is too big for `UInt` (You get 19 or fewer!)
  static func randomNumber(digitCount: Int) -> Self? {
    let digitCountDouble = Double(digitCount)

    guard digitCountDouble < log10( Double(UInt.max) ) else {
      return nil
    }

    let formatter = NumberFormatter()
    formatter.minimumIntegerDigits = digitCount
    let upperBound = pow(10, digitCountDouble)
    return formatter.string(
      for: UInt.random( in: 0..<UInt(upperBound) )
    )!
  }
}

Answer 3

func randomString(length: Int) -> String {
    return (0..<length).map { _ in String(Int.random(in: 0...9)) }.joined()
}

func randomStringBuffer(length: Int) -> String {
    var buffer = ""
    (0..<length).forEach { _ in buffer += String(Int.random(in: 0...9)) }
    return buffer
}

print(randomString(length: 15))
print(randomStringBuffer(length: 15))

first is compact, but second is more efficient, but in this situation (generating only 15 digits string) it doesn't matter, I think

UPD I made a test, and it says that I was wrong. Seems first approach, with joined() is better

let a = Date().timeIntervalSince1970
print(a)
let g = randomString(length: 10000)
let b = Date().timeIntervalSince1970
print(b)
print(b - a)



let c = Date().timeIntervalSince1970
print(c)
let f = randomStringBuffer(length: 10000)
let d = Date().timeIntervalSince1970
print(d)
print(d - c)

1583933185.788064
1583933185.9271421
0.13907814025878906 // joined() version
1583933185.927207
1583933186.2418242
0.3146171569824219 // buffer version

UPD 2 Also made a public gist also with @deep-kakkar function. As I can see, "joined()" method made it most efficient