@swift-4.2.4
struct LinearCongruentialGenerator : RandomNumberGenerator { private var seed: UInt64 init(seed: UInt64 = 0) { self.seed = seed } mutating func next() -> UInt64 { seed = 6364136223846793005 &* seed &+ 1442695040888963407 return seed } } var a = LinearCongruentialGenerator() var b = a print(a.next()) print(b.next())