Is there're a way to seed Swift 4.2 random number generator

Question

I like the new Swift 4.2 RandomNumberGenerator thing, but I don't see a seed possibility there. Am I missing something, or is there any way at all to seed these generators, by maybe calling an underlying low-level function? I have a lot of code, which uses default number generators on default number types, and I now need to make sure that everything behaves exactly the same between launches with as little code changes as possible.

Answer 1

The whole idea of the new architecture is that any generator can be substituted just by adopting the RandomNumberGenerator protocol. So if you need a repeatable seed, use your own random generator algorithm.

Answer 2

If you want reproducibility via explicit seeding you can use the GameplayKit implementation of Mersenne Twister:

import Cocoa
import GameplayKit

let mt = GKMersenneTwisterRandomSource.init(seed: 12345)

for _ in (1...5) {
  print(mt.nextUniform())
}