Swift 4: Type of expression is ambiguous without more context inside loop

Question

I have a question:

I'm retrieving a long string made of some base 64 strings attached together with ";" separating each of them inside said string.

Here's my code:

   if(item.photo != "null"){
            let b64fullstring = item.photo
            if(b64fullstring!.contains(";")){
                let photos = b64fullstring!.split(separator: ";")
                
                for pic in photos{
                    let base64encodedstring = pic
                    let decodedData = Data(base64Encoded: base64encodedstring!, options: Data.Base64DecodingOptions.ignoreUnknownCharacters)!
                    let decodedString = String(data: decodedData, encoding: .utf8)!
                    print(pic)
                }
            }
        
        
        }

Its gives me the following error on the "data" function; Type of expression is ambiguous without more context I really don't get it. When working on a single string, it works perfectly fine. But when using a loop, it gives this message for some reason.

Thank you for taking some of your time for helping me.

Leo Dabus · Accepted Answer · 2020-09-20T02:32:39.153

Swift errors are not very helpful. The problem there is that split method returns an array of substrings:

func split(separator: Character, maxSplits: Int = Int.max, omittingEmptySubsequences: Bool = true) -> [Substring]

And the Data initializer expects a String:

init?(base64Encoded base64String: String, options: Data.Base64DecodingOptions = [])

You just need to initialize a new string from your substring:

if let photos = b64fullstring?.split(separator: ";") {
    for pic in photos {
        if let decodedData = Data(base64Encoded: String(pic), options: .ignoreUnknownCharacters) {
            if let decodedString = String(data: decodedData, encoding: .utf8) {
                print(pic)
            }
        }
    }
}

Another option is to use components(separatedBy:) method which returns an array of strings instead of substrings:

func components<T>(separatedBy separator: T) -> [String] where T : StringProtocol

if let photos = b64fullstring?.components(separatedBy: ";") {
    for pic in photos {
        if let decodedData = Data(base64Encoded: pic, options: .ignoreUnknownCharacters) {
            if let decodedString = String(data: decodedData, encoding: .utf8) {
                print(pic)
            }
        }
    }
}

It was as simple as that. Thanks a lot for your detailed answer. I'm not really used to string and I found it weird for a simple split method to return something else than strings, especially if there are functions that do not work with substring. The error message could have been more specific tho. Thanks again for taking some of your time to answer, take care :) — Sutterlin Sébastien, Sep 20 '20 at 16:02

Swift 4: Type of expression is ambiguous without more context inside loop

1 Answers1