小编Hai*_*uan的帖子

我想为字符串做一个子字符串扩展,我尝试了2种方法,但不成功:

extension String
{
    func substringToFirstChar(of char: Character) -> String
    {
        let pos = self.range(of: String(char))
        let subString = self[..<pos?.lowerBound]   
        return String(subString)
    }
}

要么

extension String
{
    func substringToFirstChar(of char: Character) -> String
    {
        let pos = self.index(of: char)
        let subString = self[..<pos]
        return String(subString)
    }
}

xcode提示错误: 无法 在" let subString = self [... "行中推断出通用参数'Self'.

怎么做 ？