Parallel map in Swift

parallel_map.swift

extension Array {
  func parallelMap<T>(transform: (Element) -> T) -> [T] {
    var result = ContiguousArray<T?>(repeating: nil, count: count)
    return result.withUnsafeMutableBufferPointer { buffer in
      DispatchQueue.concurrentPerform(iterations: buffer.count) { idx in
        buffer[idx] = transform(self[idx])
      }
      return buffer.map { $0! }
    }
  }
}