swift - 调用下标 [Swift] 时没有完全匹配

Question

在这下面你可以看到我的代码。我评论了导致错误的行。错误消息:“调用下标时没有完全匹配”。你知道我怎样才能避免这个错误吗？谢谢您的帮助!

        let dic = ["a": 1, "b": 2, "c": 3, "d": 4, "e": 5, "f": 6, "g": 7, "h": 8, "i": 9, "j": 10, "k": 11, "l": 12, "m": 13, "n": 14, "o": 15, "p": 16, "q": 17, "r": 18, "s": 19, "t": 20, "u": 21, "v": 22, "w": 23, "x": 24, "y": 25, "z": 26]
        var newwrd = ""
        for var i in str ?? "" {
            let ci = dic[i]   // This line causes the error
        }

Answer 1

其实你应该得到错误

Cannot subscript a value of type '[String : Int]' with an argument of type 'String.Element' (aka 'Character')

str显然是 String? ，枚举字符串时的元素类型为 Character但订阅类型必须是 String .

let dic = ["a": 1, "b": 2, "c": 3, "d": 4, "e": 5, "f": 6, "g": 7, "h": 8, "i": 9, "j": 10, "k": 11, "l": 12, "m": 13, "n": 14, "o": 15, "p": 16, "q": 17, "r": 18, "s": 19, "t": 20, "u": 21, "v": 22, "w": 23, "x": 24, "y": 25, "z": 26]
for i in str ?? "" { // no need for var i
   let ci = dic[String(i)] ?? 0
   print(ci)
}

如果字符串包含不在字典中的字符，则结果为 0。

没有辅助字典有更短的方法

for i in str ?? "" where ("a"..."z") ~= i {
    let ci = Int(i.asciiValue!) - 96
    print(ci)
}