如何在Swift 4中使用字符串切片下标？

Question

我有以下用Swift 3编写的简单代码:

let str = "Hello, playground"
let index = str.index(of: ",")!
let newStr = str.substring(to: index)

从Xcode 9 beta 5,我得到以下警告:

' substring(to:)'已被弃用:请使用String带有'partial range from'运算符的切片下标.

如何在Swift 4中使用具有部分范围的切片下标？

Answer 1

你应该将一边留空,因此名称为"部分范围".

let newStr = str[..<index]

同样代表运营商的部分范围,只是将对方留空:

let newStr = str[index...]

请记住,这些范围运算符返回a Substring.如果要将其转换为字符串,请使用String初始化函数:

let newStr = String(str[..<index])

您可以在此处阅读有关新子串的更多信息.

Answer 2

将子串(Swift 3)转换为字符串切片(Swift 4)

示例在Swift 3,4中:

let newStr = str.substring(to: index) // Swift 3
let newStr = String(str[..<index]) // Swift 4

let newStr = str.substring(from: index) // Swift 3
let newStr = String(str[index...]) // Swift 4 

let range = firstIndex..<secondIndex // If you have a range
let newStr = = str.substring(with: range) // Swift 3
let newStr = String(str[range])  // Swift 4

Answer 3

斯威夫特4

用法

let text = "Hello world"
text[0] // H
text[...3] // "Hell"
text[6..<text.count] // world
text[NSRange(location: 6, length: 3)] // wor

码

import Foundation

public extension String {
  subscript(value: Int) -> Character {
    self[index(at: value)]
  }
}

public extension String {
  subscript(value: NSRange) -> Substring {
    self[value.lowerBound..<value.upperBound]
  }
}

public extension String {
  subscript(value: CountableClosedRange<Int>) -> Substring {
    self[index(at: value.lowerBound)...index(at: value.upperBound)]
  }

  subscript(value: CountableRange<Int>) -> Substring {
    self[index(at: value.lowerBound)..<index(at: value.upperBound)]
  }

  subscript(value: PartialRangeUpTo<Int>) -> Substring {
    self[..<index(at: value.upperBound)]
  }

  subscript(value: PartialRangeThrough<Int>) -> Substring {
    self[...index(at: value.upperBound)]
  }

  subscript(value: PartialRangeFrom<Int>) -> Substring {
    self[index(at: value.lowerBound)...]
  }
}

private extension String {
  func index(at offset: Int) -> String.Index {
    index(startIndex, offsetBy: offset)
  }
}

Answer 4

Swift 4中的缩写:

var string = "123456"
string = String(string.prefix(3)) //"123"
string = String(string.suffix(3)) //"456"

Answer 5

您可以通过以下方式将代码转换为Swift 4:

let str = "Hello, playground"
let index = str.index(of: ",")!
let substr = str.prefix(upTo: index)

您可以使用以下代码获得一个新字符串:

let newString = String(str.prefix(upTo: index))

Answer 6

substring(from:index) 转换为 [index ...]

检查样品

let text = "1234567890"
let index = text.index(text.startIndex, offsetBy: 3)

text.substring(from: index) // "4567890"   [Swift 3]
String(text[index...])      // "4567890"   [Swift 4]

Answer 7

迅捷5

（Java的子字符串方法）：

extension String {
    func subString(from: Int, to: Int) -> String {
       let startIndex = self.index(self.startIndex, offsetBy: from)
       let endIndex = self.index(self.startIndex, offsetBy: to)
       return String(self[startIndex...endIndex])
    }
}

用法：

var str = "Hello, Nick Michaels"
print(str.subString(from:7,to:20))
// print Nick Michaels

Answer 8

一些有用的扩展:

extension String {
    func substring(from: Int, to: Int) -> String {
        let start = index(startIndex, offsetBy: from)
        let end = index(start, offsetBy: to - from)
        return String(self[start ..< end])
    }

    func substring(range: NSRange) -> String {
        return substring(from: range.lowerBound, to: range.upperBound)
    }
}

Answer 9

uppercasedFirstCharacterSwift3和Swift4中的便利属性示例.

属性uppercasedFirstCharacterNew演示了如何在Swift4中使用String切片下标.

extension String {

   public var uppercasedFirstCharacterOld: String {
      if characters.count > 0 {
         let splitIndex = index(after: startIndex)
         let firstCharacter = substring(to: splitIndex).uppercased()
         let sentence = substring(from: splitIndex)
         return firstCharacter + sentence
      } else {
         return self
      }
   }

   public var uppercasedFirstCharacterNew: String {
      if characters.count > 0 {
         let splitIndex = index(after: startIndex)
         let firstCharacter = self[..<splitIndex].uppercased()
         let sentence = self[splitIndex...]
         return firstCharacter + sentence
      } else {
         return self
      }
   }
}

let lorem = "lorem".uppercasedFirstCharacterOld
print(lorem) // Prints "Lorem"

let ipsum = "ipsum".uppercasedFirstCharacterNew
print(ipsum) // Prints "Ipsum"

Answer 10

您可以使用类String的扩展创建自定义subString方法,如下所示:

extension String {
    func subString(startIndex: Int, endIndex: Int) -> String {
        let end = (endIndex - self.count) + 1
        let indexStartOfText = self.index(self.startIndex, offsetBy: startIndex)
        let indexEndOfText = self.index(self.endIndex, offsetBy: end)
        let substring = self[indexStartOfText..<indexEndOfText]
        return String(substring)
    }
}

Answer 11

使用Swift 4从String创建SubString（前缀和后缀）：

let str : String = "ilike"
for i in 0...str.count {
    let index = str.index(str.startIndex, offsetBy: i) // String.Index
    let prefix = str[..<index] // String.SubSequence
    let suffix = str[index...] // String.SubSequence
    print("prefix \(prefix), suffix : \(suffix)")
}

输出量

prefix , suffix : ilike
prefix i, suffix : like
prefix il, suffix : ike
prefix ili, suffix : ke
prefix ilik, suffix : e
prefix ilike, suffix : 

如果要在两个索引之间生成子字符串，请使用：

let substring1 = string[startIndex...endIndex] // including endIndex
let subString2 = string[startIndex..<endIndex] // excluding endIndex