我正在阅读“ The Swift Programming Language Swift 4.2”和“子字符串”部分下“字符串和字符”一章中,给出以下代码作为示例:
let greeting = "Hello, world!"
let index = greeting.firstIndex(of: ",") ?? greeting.endIndex
let beginning = greeting[..<index]
// beginning is "Hello"
// Convert the result to a String for long-term storage.
let newString = String(beginning)
我复制了此块并将其粘贴到我的Xcode游乐场中;但是,出现以下错误:
Playground execution failed:
error: MyPlayground.playground:6:13: error: value of type 'String' has
no member 'firstIndex'
let index = greeting.firstIndex(of: ",") ?? greeting.endIndex
^~~~~~~~ ~~~~~~~~~~
我检查了https://developer.apple.com/documentation/swift/string上的String类是否确实有一个名为firstIndex()的方法。
我在操场的顶部有 import UIKit; 。
您能告诉我为什么会出现此错误吗?
答案 0 :(得分:4)
您可以尝试index(of
let index = greeting.index(of: ",") ?? greeting.endIndex
在Xcode 10 beta Doc中存在firstIndex
,