函数的作用是:删除字符串的最后一个元素。

var expression = "45+22"
expression = expression.dropLast()

var str = "Hello, playground"

extension String {
    var stringByDeletingLastCharacter: String {
        return dropLast(self)
    }
}

println(str.stringByDeletingLastCharacter)   // "Hello, playgroun"

全局的dropLast()函数作用于序列，因此也作用于字符串:

var expression  = "45+22"
expression = dropLast(expression)  // "45+2"

// in Swift 2.0 (according to cromanelli's comment below)
expression = String(expression.characters.dropLast())

使用函数advance(startIndex, endIndex):

var str = "45+22"
str = str.substringToIndex(advance(str.startIndex, countElements(str) - 1))

简单回答(2015-04-16有效):removeAtIndex(mystring . endindex .前任())

例子:

var howToBeHappy = "Practice compassion, attention and gratitude. And smile!!"
howToBeHappy.removeAtIndex(howToBeHappy.endIndex.predecessor())
println(howToBeHappy)
// "Practice compassion, attention and gratitude. And smile!"

元:

语言继续着它的快速进化，使得许多以前很好的sos答案的半衰期变得危险地短暂。学习语言并参考真正的文档总是最好的。

另一种方法如果你想从末尾删除一个或多个字符。

var myStr = "Hello World!"
myStr = (myStr as NSString).substringToIndex((myStr as NSString).length-XX)

其中XX是要删除的字符数。