斯威夫特 4.0(也是斯威夫特 5.0)
var str = "Hello, World" // "Hello, World"
str.dropLast() // "Hello, Worl" (non-modifying)
str // "Hello, World"
String(str.dropLast()) // "Hello, Worl"
str.remove(at: str.index(before: str.endIndex)) // "d"
str // "Hello, Worl" (modifying)
斯威夫特3.0
API 变得更多了一些swifty,因此基金会扩展发生了一些变化:
var name: String = "Dolphin"
var truncated = name.substring(to: name.index(before: name.endIndex))
print(name) // "Dolphin"
print(truncated) // "Dolphi"
或者就地版本:
var name: String = "Dolphin"
name.remove(at: name.index(before: name.endIndex))
print(name) // "Dolphi"
谢谢兹梅,罗布·艾伦!
Swift 2.0+ 方式
有几种方法可以实现此目的:
通过 Foundation 扩展,尽管不是 Swift 库的一部分:
var name: String = "Dolphin"
var truncated = name.substringToIndex(name.endIndex.predecessor())
print(name) // "Dolphin"
print(truncated) // "Dolphi"
使用removeRange()
方法(其中alters the name
):
var name: String = "Dolphin"
name.removeAtIndex(name.endIndex.predecessor())
print(name) // "Dolphi"
使用dropLast()
功能:
var name: String = "Dolphin"
var truncated = String(name.characters.dropLast())
print(name) // "Dolphin"
print(truncated) // "Dolphi"
旧的 String.Index (Xcode 6 Beta 4 +) 方式
Since String
Swift 中的类型旨在提供出色的 UTF-8 支持,您不能再使用访问字符索引/范围/子字符串Int
类型。相反,你使用String.Index
:
let name: String = "Dolphin"
let stringLength = count(name) // Since swift1.2 `countElements` became `count`
let substringIndex = stringLength - 1
name.substringToIndex(advance(name.startIndex, substringIndex)) // "Dolphi"
或者(对于更实用但教育性较低的示例)您可以使用endIndex
:
let name: String = "Dolphin"
name.substringToIndex(name.endIndex.predecessor()) // "Dolphi"
Note:我发现this https://stackoverflow.com/a/24056932/88111成为理解的一个很好的起点String.Index
旧的(Beta 4 之前)方式
您可以简单地使用substringToIndex()
函数,提供它的长度小于String
:
let name: String = "Dolphin"
name.substringToIndex(countElements(name) - 1) // "Dolphi"