这个 func swap 函数（ Swift 实现）该如何理解？

[GromHellscream]

fileprivate func reverse<T>(_ chars: inout [T], _ start: Int, _ end: Int) {
  var start = start, end = end

  while start < end {
    swap(&chars, start, end)
    start += 1
    end -= 1
  }
}

fileprivate func swap<T>(_ chars: inout [T], _ p: Int, _ q: Int) {
  (chars[p], chars[q]) = (chars[q], chars[p]) //请问，这一行该怎么理解？
}

[GromHellscream]

https://imgur.com/emTEW9H