Dice example in swift

Dice.swift

protocol RandomNumberGenerator {
    func random() -> Double
}

class LinearCongruentialGenerator : RandomNumberGenerator {
    var lastRandom = 42.0
    let m = 139969.0
    let a = 3877.0
    let c = 29573.0
    func random() -> Double {
        lastRandom = ((lastRandom * a + c) % m)
        return lastRandom / m
    }
}

class Dice {
    let sides: Int
    let generator: RandomNumberGenerator
    init(sides: Int, generator: RandomNumberGenerator) {
        self.sides = sides
        self.generator = generator
    }
    func roll() -> Int {
        return Int(generator.random() * Double(sides
            )) + 1
    }
}

let dice = Dice(sides: 6, generator: LinearCongruentialGenerator())
dice.roll()