Swift 数组：带 IndexPath 的下标 - 无法改变

Question

我想向数组的数组添加扩展以检索具有 IndexPath 大小为 2:

的 Element

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

我在实现以下扩展时遇到错误无法通过下标分配下标是仅获取:

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？如何向下标添加突变选项？

Answer 1

为了改变嵌套数组，你必须要求

Element : MutableCollection

而不是 Element : Collection。

你还可以定义两个扩展名：一个只读下标为只读集合，以及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
        }
    }
}

Swift 数组：带 IndexPath 的下标 - 无法改变

Swift Array: subscript with IndexPath - unable to mutate

arrays

collections

subscript

ios

swift