No exact matches in call to subscript [Swift]

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Underneath this you can see my code. I commented the line which causes the error. Error message: "No exact matches in call to subscript". Do you know how I can avoid this error? Thank you for your help!

        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
        }
swift for-loop dictionary input
2 Answers

Actually you should get the error

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

str is obviously String?, the element type when enumerating a string is Character but the subscription type must be 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)
}

If the string contains a character which is not in the dictionary the result is 0.

There is a shorter way without a helper dictionary

for i in str ?? "" where ("a"..."z") ~= i {
    let ci = Int(i.asciiValue!) - 96
    print(ci)
}
user_50440420

As @vadian says, it looks like str is an Optional<String>. Looping through a string gives you Characters, but your dictionary keys are Strings. You need to convert each character to a String, and deal with optionals. Try this code:

let str: String? = "abcqrml@"
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 i in str ?? "" {
    if let ci = dic[String(i)] {
        print("dic[\(i)] = \(ci)")
    }  else {
        print("dic[\(i)] = nil")
    }
}
user_2051850
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