Eratosthenes.swift

typealias A = ArraySlice<Bool>
func sieveOfEratosthenes(limit: Int) -> [Int] {
  var possibles = A(repeating: true, count: limit + 1)
  var result = [Int]()
  for i in 2 ... limit {
    guard possibles[i] else { continue }
    for j in stride(from: i * i, through: limit, by: i) {
        possibles[j] = false
    }
    result.append(i)
  }
  return result
}