Swift Array：帶IndexPath的下標 - 無法變異

Question

我想為數組數組添加一個擴展來檢索IndexPath大小為2的Element ：

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

我得到一個錯誤無法通過下標下標分配是get-only同時實現以下擴展：

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
    }
  }
}

出現這種錯誤的原因是什么？ 如何在下標中添加變異選項？

Answer 1

為了改變嵌套數組，你必須要求它

Element : MutableCollection

而不是Element : Collection 。

您還可以定義兩個擴展：只讀集合的​​只讀下標和可變集合的讀寫下標：

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
        }
    }
}