swift - removeSubrange 产生 '()' ，而不是预期的上下文结果类型 'String'

Question

static func trimBefore(string: inout String, char: Character) -> String {

    var newString = ""

    if let charRange = string.range(of: String(char)) {
        newString = string.removeSubrange(string.startIndex..<charRange.upperBound)
    }
    return newString
}

static func trimAfter(string: inout String, char: Character) -> String {

    var newString = ""

    if let charRange = string.range(of: String(char)) {
        newString = string.removeSubrange(charRange.lowerBound..<string.endIndex)
    }
    return newString
}

我在标题中遇到了错误。为什么会这样？

Answer 1

当我尝试 print(extInfo.trimBefore(char: ".") 时问题开始了。这返回了 ()。

当我把它改成:

extInfo.trimAfter(char: ".")
print(extInfo)

它按预期工作。

mutating func trimBefore(char: Character) {

    if let charRange = self.range(of: String(char)) {
        self.removeSubrange(self.startIndex..<charRange.upperBound)
    }
}

mutating func trimAfter(char: Character) {

    if let charRange = self.range(of: String(char)) {
        self.removeSubrange(charRange.lowerBound..<self.endIndex)
    }
}