How does one generate a random number in Swift?

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?

Swift 4.2+

Swift 4.2 shipped with Xcode 10 introduces new easy-to-use random functions for many data types.
You can call the random() method on numeric types.

let randomInt = Int.random(in: 0..<6)
let randomDouble = Double.random(in: 2.71828...3.14159)
let randomBool = Bool.random()