如何在swift3中增加String.Index？

Question

In swift2.3 ++ operator use for string.index increase

eg. i++

I changed to swift 3 that code happen " Unary operator '++' cannot be applied to an operand of type '@lvalue String.Index' (aka '@lvalue String.CharacterView.Index') " in swift 3

I rewrite eg. i += 1

but this code can't solve. Please Help me.

Answer 1

String.Index is a typealias for String.CharacterView.Index . The index cannot, on its own, be increased. Rather, you can use the index(after:) instance method on the CharacterView that you used to extract the index.

Eg:

let str = "foobar"
let chars = str.characters

if let bIndex = chars.index(of: "b") {
    let nextIndex = chars.index(after: bIndex)
    print(str[bIndex...nextIndex]) // ba
}

Or, given that you have an index (eg str.startIndex ), you can use the index(_:, offsetBy:) instance method available also directly for String instances:

let str = "foobar"
let startIndex = str.startIndex
let nextIndex = str.index(startIndex, offsetBy: 1)
print(str[startIndex...nextIndex]) // fo

Answer 2

String.Index doesn't have a ++ , += , or any kind of operator (other than comparisons, eg < , > , == ) defined for it. It has other methods defined for moving the index. To increase the index 1 position, the code would look like this: string.index(i, offsetBy: 1)

let string = "Some string"
var i = string.startIndex
i = string.index(i, offsetBy: 1)