SwiftTip14.swift

actor DiapasonTracker {
  private var minValue: Int = 0
  private var maxValue: Int = 0

  func receive(_ batch: [Int]) {
    guard let batchMin = batch.min() else { return }
    minValue = min(minValue, batchMin)
    guard let batchMax = batch.max() else { return }
    maxValue = max(maxValue, batchMax)
  }

  // Here diapason can't be accessed
  // at the same time when receive() is
  // the middle of updating
  // minValue and/or maxValue.
  // Using class instead of actor would
  // allow one thread to update values
  // while another is accessing diapason
  // property which leads to inconsistencies.
  var diapason: Int {
    maxValue - minValue
  }
}