通过可选绑定在Swift中进行安全（边界检查）数组查找？

Alex的回答为该问题提供了很好的建议和解决方案，但是，我偶然发现了一种更好的实现此功能的方法：

Swift 3.2及更高版本

extension Collection {    /// Returns the element at the specified index if it is within bounds, otherwise nil.    subscript (safe index: Index) -> Element? {        return indices.contains(index) ? self[index] : nil    }}

Swift 3.0和3.1

extension Collection where Indices.Iterator.Element == Index {    /// Returns the element at the specified index if it is within bounds, otherwise nil.    subscript (safe index: Index) -> Generator.Element? {        return indices.contains(index) ? self[index] : nil    }}

感谢Hamish提出了Swift 3解决方案。

迅捷2

extension CollectionType {    /// Returns the element at the specified index if it is within bounds, otherwise nil.    subscript (safe index: Index) -> Generator.Element? {        return indices.contains(index) ? self[index] : nil    }}

例

let array = [1, 2, 3]for index in -20...20 {    if let item = array[safe: index] {        print(item)    }}