Swift Array:带IndexPath的下标 - 无法变异

Question

我想的扩展名添加到阵列的阵列,以检索Element与所述IndexPath大小为2:

let array: [[String]] =  ....
let indexPath = IndexPath(indexes: [0, 0])
let string = array[indexPath]

我得到一个错误无法通过下标下标分配是get-only同时实现以下扩展:

extension Array where Element : Collection, Element.Index == Int {
  subscript(indexPath: IndexPath) -> Element.Iterator.Element {
    get {
      return self[indexPath.section][indexPath.item]
    }
    set {
      self[indexPath.section][indexPath.item] = newValue
    }
  }
}

出现这种错误的原因是什么？如何在下标中添加变异选项 ？

Answer 1

为了改变嵌套数组,你必须要求它

Element : MutableCollection

而不是Element : Collection.

您还可以定义两个扩展:只读集合的​​只读下标和可变集合的读写下标:

extension Collection where Index == Int, Element : Collection, Element.Index == Int {
    subscript(indexPath: IndexPath) -> Element.Iterator.Element {
        return self[indexPath[0]][indexPath[1]]
    }
}

extension MutableCollection where Index == Int, Element : MutableCollection, Element.Index == Int {
    subscript(indexPath: IndexPath) -> Element.Iterator.Element {
        get {
            return self[indexPath[0]][indexPath[1]]
        }
        set {
            self[indexPath[0]][indexPath[1]] = newValue
        }
    }
}