swift 从字符串中获取char

Posted 2021-05-19

extension String {
    
    subscript (i: Int) -> Character {
        return self[self.characters.index(self.startIndex, offsetBy: i)]
    }
    
    subscript (i: Int) -> String {
        return String(self[i] as Character)
    }
    
    subscript (r: Range<Int>) -> String {
        let start = characters.index(startIndex, offsetBy: r.lowerBound)
        let end = characters.index(start, offsetBy: r.upperBound - r.lowerBound)
        return String(self[Range(start ..< end)])
    }
}