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()

对于swift 5，你可以简单地这样做:

为字符串创建扩展:

extension String {
    var firstUppercased: String {
        let firstChar = self.first?.uppercased() ?? ""
        return firstChar + self.dropFirst()
    }
}

then

yourString.firstUppercased

样本:"abc" -> "abc"

extension String {
    var lowercased:String {
        var result = Array<Character>(self.characters);
        if let first = result.first { result[0] = Character(String(first).uppercaseString) }
        return String(result)
    }
}

字符串中的第一个字符大写

extension String {
    var capitalizeFirst: String {
        if self.characters.count == 0 {
            return self

        return String(self[self.startIndex]).capitalized + String(self.characters.dropFirst())
    }
}

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())
    }
}

我用柯尔斯泰因斯解得到了第一个复制的字符。这将大写第一个字符，不会看到双字符:

var s: String = "hello world"
s = prefix(s, 1).capitalizedString + suffix(s, countElements(s) - 1)

我不知道它的效率是高还是低，我只知道它给了我想要的结果。