我的解决方案:

func firstCharacterUppercaseString(string: String) -> String {
    var str = string as NSString
    let firstUppercaseCharacter = str.substringToIndex(1).uppercaseString
    let firstUppercaseCharacterString = str.stringByReplacingCharactersInRange(NSMakeRange(0, 1), withString: firstUppercaseCharacter)
    return firstUppercaseCharacterString
}

在swift 5中

https://www.hackingwithswift.com/example-code/strings/how-to-capitalize-the-first-letter-of-a-string

extension String {
    func capitalizingFirstLetter() -> String {
        return prefix(1).capitalized + dropFirst()
    }

    mutating func capitalizeFirstLetter() {
        self = self.capitalizingFirstLetter()
    }
}

和你的绳子一起使用

let test = "the rain in Spain"
print(test.capitalizingFirstLetter())

我更喜欢这个版本，它是从另一个答案中清理出来的版本:

extension String {
  var capitalizedFirst: String {
    let characters = self.characters
    if let first = characters.first {
      return String(first).uppercased() + 
             String(characters.dropFirst())
    }
    return self
  }
}

它努力通过只评估自我来提高效率。字符一次，然后使用一致的形式创建子字符串。

包括与API准则一致的突变和非突变版本。

斯威夫特3:

extension String {
    func capitalizingFirstLetter() -> String {
        let first = String(characters.prefix(1)).capitalized
        let other = String(characters.dropFirst())
        return first + other
    }

    mutating func capitalizeFirstLetter() {
        self = self.capitalizingFirstLetter()
    }
}

斯威夫特4:

extension String {
    func capitalizingFirstLetter() -> String {
      return prefix(1).uppercased() + self.lowercased().dropFirst()
    }

    mutating func capitalizeFirstLetter() {
      self = self.capitalizingFirstLetter()
    }
}

Swift 3 (xcode 8.3.3)

大写字符串的所有首字符

let str = "your string"
let capStr = str.capitalized

//Your String

全部大写

let str = "your string"
let upStr = str.uppercased()

//YOUR STRING

字符串的第一个字符只能大写

 var str = "your string"
 let capStr = String(str.characters.prefix(1)).uppercased() + String(str.characters.dropFirst())

//Your string

Leonardo Savio Dabus:

我想大多数用例是获得适当的套管:

import Foundation

extension String {

    var toProper:String {
        var result = lowercaseString
        result.replaceRange(startIndex...startIndex, with: String(self[startIndex]).capitalizedString)
        return result
    }
}