Question

我想向数组数组添加扩展，以检索 IndexPath 大小为2的Element：

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

在实现以下扩展时，我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 } } }

这种错误的原因是什么？如何为下标添加一个突变选项？

Answer 1

要变异嵌套数组，您必须要求

Element : MutableCollection

代替Element : Collection。

您还可以定义两个扩展名：只读的只读下标集合，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：带有IndexPath的下标-无法突变

1 个答案: