在swift 3中，你如何推进一个指数?

I've trying to get a substring of a string starting from index 1 in iOS 10 beta 6, and its a headache as swifts strings are constantly changing and much documentation is out of date and useless.

我试着从ios10 beta 6的索引1中获取一个字符串的子字符串，它让人头痛，因为swift字符串不断变化，很多文档都过时了，毫无用处。

String has the substring(from:Index), but it can't accept an integer (which has been the case for a while), so I was planning to use startIndex and advance it by 1, but now Index has no advanceBy method, so I cannot do this:

字符串有子字符串(from:Index)，但是它不能接受整数(这在一段时间内是这样的)，所以我打算使用startIndex并将其提前1，但是现在索引没有方法，所以我不能这样做:

let aString = "hello"
let subString = aString.substring(from: aString.startIndex.advanceBy(1))

How can I get a substring from index 1? How can you advance an index these days, and what is the point of the substring(from Index) method - how are you supposed to use it?

如何从索引1获得子字符串?如何在这些天内提高索引，以及子字符串(从索引)方法的要点是什么?您应该如何使用它?

2 个解决方案

#1

Looks pretty clear as the first item in the Swift 3 migration guide:

看起来很清楚，作为Swift 3迁移指南中的第一项:

The most visible change is that indexes no longer have successor(), predecessor(), advancedBy(_:), advancedBy(_:limit:), or distanceTo(_:) methods. Instead, those operations are moved to the collection, which is now responsible for incrementing and decrementing its indices.

最明显的变化是索引不再具有继承者()、前辈()、advancedBy(_:)、advancedBy(_:limit:)或distanceTo(_:)方法。相反，这些操作被转移到集合中，该集合现在负责对其索引进行递增和递减。

myIndex.successor()  =>  myCollection.index(after: myIndex)
myIndex.predecessor()  =>  myCollection.index(before: myIndex)
myIndex.advance(by: …) => myCollection.index(myIndex, offsetBy: …)

So it looks like you want something like:

所以看起来你想要的是:

let greeting = "hello"
let secondCharIndex = greeting.index(after: greeting.startIndex)
let enryTheEighthGreeting = greeting.substring(from: secondCharIndex) // -> "ello"

(Note also that if you want Collection functionality—like index management—on a String, it sometimes helps to use its characters view. String methods like startIndex and index(after:) are just conveniences that forward to the characters view. That part isn't new, though... Strings stopped being Collections themselves in Swift 2 IIRC.)

(还要注意，如果想要在字符串上收集功能类似的索引管理，它有时会帮助使用它的字符视图。像startIndex和index(after:)这样的字符串方法只是对字符视图的方便。那部分并不新鲜，不过……在Swift 2 IIRC中，字符串不再是集合本身。

There's more about the collection indexes change in SE-0065 - A New Model for Collections and Indices.

在SE-0065中有更多关于集合索引的变化——一个新的集合和索引模型。

#2

Swift 3:

let str = "hello"
let subStr = str.substring(from:str.index(str.startIndex,offsetBy: 1))
print(subStr)//ello

Less verbose solution:

更少的详细解决方案:

print(str.substring(from:str.idx(index)))//ello
extension String{
    func idx(_ index:Int) -> String.Index{
        return self.index(self.startIndex, offsetBy: index)
    }
}