String

字符串索引

let greeting = "swift"

greeting[greeting.startIndex]

greeting[greeting.index(before:greeting.endIndex)]

greeting[greeting.index(after:greeting.startIndex)]

let index = greeting.index(greeting.startIndex,offsetBy:3)

greeting[index]

插入与删除

let greeting = "swift"
greeting[greeting.index(before: greeting.endIndex)]

var greet = "swift"
greet.insert("!", at: greet.endIndex)
greet.insert(contentsOf: " to you ", at: greet.index(before: greet.endIndex))

let a = greet.remove(at: greet.index(before: greet.endIndex))
let range = greet.index(greet.endIndex, offsetBy: -3)..<greet.endIndex
greet.removeSubrange(range)

Substring

    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)