下面是我一小步一小步完成的方法，类似于@Kirsteins。

func capitalizedPhrase(phrase:String) -> String {
    let firstCharIndex = advance(phrase.startIndex, 1)
    let firstChar = phrase.substringToIndex(firstCharIndex).uppercaseString
    let firstCharRange = phrase.startIndex..<firstCharIndex
    return phrase.stringByReplacingCharactersInRange(firstCharRange, withString: firstChar)
}

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()
    }
}

对于单词使用中的第一个字符。在swift中大写，对于整个单词使用。大写()

Swift 3更新

replaceRange函数现在是replaceSubrange

nameOfString.replaceSubrange(nameOfString.startIndex...nameOfString.startIndex, with: String(nameOfString[nameOfString.startIndex]).capitalized)

从Swift 3你可以很容易地使用 文本框。autocapitalizationType = uitextautocapitalizationtype .sentence

extension String {
    func firstCharacterUpperCase() -> String? {
        let lowercaseString = self.lowercaseString

        return lowercaseString.stringByReplacingCharactersInRange(lowercaseString.startIndex...lowercaseString.startIndex, withString: String(lowercaseString[lowercaseString.startIndex]).uppercaseString)
    }
}

let x = "heLLo"
let m = x.firstCharacterUpperCase()

对于Swift 5:

extension String {
    func firstCharacterUpperCase() -> String? {
        guard !isEmpty else { return nil }
        let lowerCasedString = self.lowercased()
        return lowerCasedString.replacingCharacters(in: lowerCasedString.startIndex...lowerCasedString.startIndex, with: String(lowerCasedString[lowerCasedString.startIndex]).uppercased())
    }
}