Random data generation in Swift
Swift Other



Platform Language: Swift CocoaPods - RandomKit Carthage GITTER: join chat codebeat badge License

RandomKit is a Swift framework that makes random data generation simple and easy.



  • Platforms:
    • macOS 10.9+
    • iOS 8.0+
    • watchOS 2.0+
    • tvOS 9.0+
    • Linux
  • Xcode 8.0
  • Swift 3.0

RandomKit is possibly also compatible with FreeBSD, Android, and Windows (under Cygwin) but has not been tested for those platforms.

Install Using Swift Package Manager

The Swift Package Manager is a decentralized dependency manager for Swift.

  1. Add the project to your Package.swift.

    import PackageDescription
    let package = Package(
        name: "MyAwesomeProject",
        dependencies: [
            .Package(url: "https://github.com/nvzqz/RandomKit.git",
                     majorVersion: 3)
  2. Import the RandomKit module.

    import RandomKit

Install Using CocoaPods

CocoaPods is a centralized dependency manager for Objective-C and Swift. Go here to learn more.

  1. Add the project to your Podfile.

    pod 'RandomKit', '~> 3.0.0'

    If you want to be on the bleeding edge, replace the last line with:

    pod 'RandomKit', :git => 'https://github.com/nvzqz/RandomKit.git'
  2. Run pod install and open the .xcworkspace file to launch Xcode.

  3. Import the RandomKit framework.

    import RandomKit

Install Using Carthage

Carthage is a decentralized dependency manager for Objective-C and Swift.

  1. Add the project to your Cartfile.

    github "nvzqz/RandomKit"
  2. Run carthage update and follow the additional steps in order to add RandomKit to your project.

  3. Import the RandomKit framework.

    import RandomKit


Various components of RandomKit can be easily benchmarked by running benchmark.sh.

./benchmark.sh [FLAGS] [PROTOCOLS]

Use the --help flag for information regarding how to use it.

Note: The default count is 10000000, which is A LOT if using the --array flag. This can be changed by passing an argument into --count or -c.


Try it out for yourself! Download the repo and open 'RandomKit.playground'.


The RandomGenerator enum is used by all random- methods and functions for specifying the random generator to use.

Available Generators:

  • arc4Random

  • device (reads from "/dev/random" or "/dev/urandom")

  • xoroshiro

  • mersenneTwister

The default random generator is specified with RandomGenerator.default and can be changed. It is initially xoroshiro(threadSafe: true).

Because the arc4Random family of functions isn't available on most Linux distros, using this case will do nothing on Linux.

Although there are randomize methods publicly available, they're used internally throughout the library.


RandomKit is very protocol-oriented, which gives it the ability to perform many neat tasks.


A protocol for types that can generate random values.


A protocol for types that can generate optional random values within a range.


A protocol for types that can generate random values within a closed ranges.

Int.random(within: -100...100)       // -79
Character.random(within: "a"..."z")  // "f"


A protocol for types that can generate random values from a base value to another value, noninclusive.

The base value for integers is 0. This means that calling random(to:) on a negative value will yield a random negative value or zero whereas a positive value will yield a random positive value or zero.

If value == randomBase, value will be returned for random(to:).

Int.random(to:  2)  // Either 0 or 1
Int.random(to:  0)  // Always 0
Int.random(to: 32)  // 15
Int.random(to: -5)  // -3


A protocol for types that can generate random values from a base value through another value, inclusive.

The same rules for the base value of RandomToMax apply to RandomThroughMax.


A protocol for types whose elements can be shuffled.

// Array
[1, 2, 3, 4, 5].shuffled()  // [3, 4, 1, 5, 2]

// Dictionary
["a": 1, "b": 2, "c": 3].shuffled()  // ["a": 3, "b": 1, "c": 2]

The mutable counterpart of shuffled() is shuffle().

Swift Types


All of Swift's native integer types conform to the Random- protocols.

The random() and random(using:) functions create an integer of any value. As a result, negative values can result for signed integers.

Int.random()                 // An Int within Int.min and Int.max
Int.random(within: 10...20)  // An Int within 10 and 20

To create a positive signed integer, use random(to:) or random(through:).

Int.random(to: 1000)     // 731
Int.random(through: 10)  // 4

Signed integers can be created from any range, without danger of overflow.

Int.random(within: (.min + 1000)...(.max - 200))  // 5698527899712144154

Floating Point Numbers

Generate a random floating point value from within a range or 0.0...1.0 by default.

Double.random()                   //  0.9813615573117475
Double.random(within:  -10...10)  // -4.03042337718197
Float.random(within:   -10...10)  //  5.167088
Float80.random(within: -10...10)  // -3.63204542399198874

All FloatingPoint types can also conform to RandomWithinClosedRange out-of-the-box.


Bool.random() has a 50/50 chance of being true for the default generator.

String, Character, and UnicodeScalar

String, Character, and UnicodeScalar generate values within " "..."~" by default.

String.random(ofLength: 10)                     // "}+[=Ng>$w1"
String.random(ofLength: 10, within: "A"..."z")  // "poUtXJIbv["

Character.random()                   // "#"
Character.random(within: "A"..."z")  // "s"

Sequence and Collection

All types that conform to Sequence and/or Collection have a random property that returns a random element, or nil if the collection is empty.

["Bob", "Cindy", "May", "Charles", "Javier"].random  // "Charles"

"Hello".characters.random  // "e"

Even Foundation types that conform to either protocol get this property.

NSDictionary(dictionary: ["k1":"v1", "k2":"v2"]).random      // (k1, v1)

NSSet(array: ["First", "Second", "Third", "Fourth"]).random  // "Third"


An array of random values can be generated for types conforming to Random using init(randomCount:).

Similar initializers exist for RandomWithinRange and RandomWithinClosedRange.

let randoms = Array<Int>(randomCount: 100)  // [[8845477344689834233, -957454203475087100, ...]

For types conforming to UnsafeRandom, a faster alternative is init(unsafeRandomCount:using:). This initializer fills the buffer directly rather than using random().

let unsafeRandoms = Array<Int>(unsafeRandomCount: 100)  // [759709806207883991, 4618491969012429761, ...]
Arrays Benchmark

A benchmark of generating 1000 random arrays of 10000 count:

Generator Safe (seconds) Unsafe (seconds)
xoroshiro(threadSafe: false) 3.4709 0.1068
xoroshiro(threadSafe: true) 3.9388 0.1059
mersenneTwister(threadSafe: false) 3.4346 0.1160
mersenneTwister(threadSafe: true) 3.5670 0.1215
arc4Random 6.6060 0.3336
device(random) 67.7667 5.7254
device(urandom) 71.0310 5.7347

Note: Results may vary due to various factors.

This benchmark can be run with:

./benchmark.sh --all-generators --array 10000 --count 1000

Foundation Types


Generate a random URL from a list of values.

URL.random()  // https://medium.com/
              // https://stackoverflow.com/
              // https://github.com/
              // ...


A random Date can be generated between two Date or TimeInterval values.

The default random() function returns a Date within Date.distantPast and Date.distantFuture.

Date.random()  // "Aug 28, 2006, 3:38 AM"
Date.random(within: Date.distantPast...Date())  // "Feb 7, 472, 5:40 AM"


The Decimal type conforms to RandomWithinClosedRange.

The random() function returns a Decimal between 0 and 1 by default.

Decimal.random()                    // 0.87490000409886706715888973957833129437
Decimal.random(within: 0.0...10.0)  // 6.5464639772070720738747790627821299859


A random number can be generated from within an integer or double range, or 0...100 by default.

NSNumber.random()                   // 79
NSNumber.random(within: -50...100)  // -27
NSNumber.random(within: 0...200.0)  // 149.6156950363926

Cocoa and UIKit Types

NSColor and UIColor

A random color can be generated, with or without random alpha.

NSColor.random()            // r 0.694 g 0.506 b 0.309 a 1.0
NSColor.random(alpha: true) // r 0.859 g 0.57  b 0.409 a 0.047

UIColor.random()            // r 0.488 g 0.805 b 0.679 a 1.0
UIColor.random(alpha: true) // r 0.444 g 0.121 b 0.602 a 0.085

CoreGraphics Types


Because CGFloat conforms to FloatingPoint, it conforms to RandomWithinClosedRange just like how Double and Float do.

CGFloat.random()         // 0.699803650379181
CGFloat.random(0...100)  // 43.27969591675319


A random point can be generated from within ranges for x and y.

CGPoint.random()                         // {x 70.093 y 95.721}
CGPoint.random(within: 0...200, 0...10)  // {x 73.795 y 0.991}


A random size can be generated from within ranges for width and height.

CGSize.random()                         // {w 3.744  h 35.932}
CGSize.random(within: 0...50, 0...400)  // {w 38.271 h 239.636}


A random rectangle can be generated from within ranges for x, y, width, and height.

CGRect.random()                                         // {x 3.872  y 46.15  w 8.852  h 20.201}
CGRect.random(within: 0...50, 0...100, 0...25, 0...10)  // {x 13.212 y 79.147 w 20.656 h 5.663}


A random vector can be generated from within ranges for dx and dy.

CGVector.random()                        // {dx 13.992 dy 89.376}
CGVector.random(within: 0...50, 0...10)  // {dx 35.224 dy 13.463}



RandomKit extensions for Károly's BigInt library are available in RandomKitBigInt.


RandomKit and its assets are released under the MIT License. Assets can be found in the assets branch.