结合上面的答案，我写了一个小扩展，大写每个单词的第一个字母(因为这是我正在寻找的，并认为其他人可以使用它)。

我谦卑地提出:

extension String {
    var wordCaps:String {
        let listOfWords:[String] = self.componentsSeparatedByString(" ")
        var returnString: String = ""
        for word in listOfWords {
            if word != "" {
                var capWord = word.lowercaseString as String
                capWord.replaceRange(startIndex...startIndex, with: String(capWord[capWord.startIndex]).uppercaseString)
                returnString = returnString + capWord + " "
            }
        }
        if returnString.hasSuffix(" ") {
            returnString.removeAtIndex(returnString.endIndex.predecessor())
        }
        return returnString
    }
}

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
    }
}

Swift 5.1或更高版本

extension StringProtocol {
    var firstUppercased: String { prefix(1).uppercased() + dropFirst() }
    var firstCapitalized: String { prefix(1).capitalized + dropFirst() }
}

斯威夫特5

extension StringProtocol {
    var firstUppercased: String { return prefix(1).uppercased() + dropFirst() }
    var firstCapitalized: String { return prefix(1).capitalized + dropFirst() }
}

"Swift".first  // "S"
"Swift".last   // "t"
"hello world!!!".firstUppercased  // "Hello world!!!"

"DŽ".firstCapitalized   // "Dž"
"Dž".firstCapitalized   // "Dž"
"dž".firstCapitalized   // "Dž"

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()
    }
}

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
}

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。