你如何在swift中生成一个随机数？

根据Apple发布的书,这似乎是Swift生成随机数的方式.

protocol RandomNumberGenerator {
    func random() -> Double
}
class LinearCongruentialGenerator: RandomNumberGenerator {
    var lastRandom = 42.0
    let m = 139968.0
    let a = 3877.0
    let c = 29573.0
    func random() -> Double {
        lastRandom = ((lastRandom * a + c) % m)
        return lastRandom / m
    }
}
let generator = LinearCongruentialGenerator()

for _ in 1..10 {
    // Generate "random" number from 1-10
    println(Int(generator.random() * 10)+1)
}

问题是,在我放在底部的for循环中,输出如下所示：

4
8
7
8
6
2
6
4
1

无论我运行多少次,每次输出都是相同的.