What is the Swift equivalent of Java's Random class (isolated PRNG)

Most discussions of random number generation in Swift talk about arc4random() and other standard C functions that produce a global sequences of random numbers. In some cases it is useful to have an isolated pseudorandom number generator that provides separate, reproducible streams of numbers. e.g. in a game you may wish to have a reproducible random sequences for two aspects of the game and the order in which the two are called should not change the respective streams.

Answer:

The rand_r() function accomplishes this by operating on its own seed value to maintain state. Here is a simple example of how one could mimic the Java Random class with this.

/** Java style PRNG */
public class Random
{
    var seed : UInt32 = 0

    init( _ seed : UInt32 ) {
        self.seed = seed
    }

    /** float 0-1.0 */
    public func nextFloat() -> Float {
        return Float(rand_r(&seed)) / Float(INT32_MAX);
    }

}