How does one generate a random number in Apple'

Question

I realize the Swift book provided an implementation of a random number generator. Is the best practice to copy and paste this implementation in one's own program? Or is there a library that does this that we can use now?

Answer 1

I use this code to generate a random number:

//
//  FactModel.swift
//  Collection
//
//  Created by Ahmadreza Shamimi on 6/11/16.
//  Copyright © 2016 Ahmadreza Shamimi. All rights reserved.
//

import GameKit

struct FactModel {

    let fun  = ["I love swift","My name is Ahmadreza","I love coding" ,"I love PHP","My name is ALireza","I love Coding too"]


    func getRandomNumber() -> String {

        let randomNumber  = GKRandomSource.sharedRandom().nextIntWithUpperBound(fun.count)

        return fun[randomNumber]
    }
}

Answer 2

In Swift 4.2 you can generate random numbers by calling the random() method on whatever numeric type you want, providing the range you want to work with. For example, this generates a random number in the range 1 through 9, inclusive on both sides

let randInt = Int.random(in: 1..<10)

Also with other types

let randFloat = Float.random(in: 1..<20)
let randDouble = Double.random(in: 1...30)
let randCGFloat = CGFloat.random(in: 1...40)

Answer 3

You can use GeneratorOf like this:

var fibs = ArraySlice([1, 1])
var fibGenerator = GeneratorOf{
    _ -> Int? in
    fibs.append(fibs.reduce(0, combine:+))
    return fibs.removeAtIndex(0)
}

println(fibGenerator.next())
println(fibGenerator.next())
println(fibGenerator.next())
println(fibGenerator.next())
println(fibGenerator.next())
println(fibGenerator.next())

Answer 4

You can do it the same way that you would in C:

let randomNumber = arc4random()

randomNumber is inferred to be of type UInt32 (a 32-bit unsigned integer)

Answer 5

Edit for Swift 4.2

Starting in Swift 4.2, instead of using the imported C function arc4random_uniform(), you can now use Swift’s own native functions.

// Generates integers starting with 0 up to, and including, 10
Int.random(in: 0 ... 10)

You can use random(in:) to get random values for other primitive values as well; such as Int, Double, Float and even Bool.

Swift versions < 4.2

This method will generate a random Int value between the given minimum and maximum

func randomInt(min: Int, max: Int) -> Int {
    return min + Int(arc4random_uniform(UInt32(max - min + 1)))
}

Answer 6

I would like to add to existing answers that the random number generator example in the Swift book is a Linear Congruence Generator (LCG), it is a severely limited one and shouldn't be except for the must trivial examples, where quality of randomness doesn't matter at all. And a LCG should never be used for cryptographic purposes.

arc4random() is much better and can be used for most purposes, but again should not be used for cryptographic purposes.

If you want something that is guaranteed to be cryptographically secure, use SecCopyRandomBytes(). Note that if you build a random number generator into something, someone else might end up (mis)-using it for cryptographic purposes (such as password, key or salt generation), then you should consider using SecCopyRandomBytes() anyway, even if your need doesn't quite require that.