Dictionary extension in Swift is not recognized

Question

I am trying to extend Dictionary with the following code:

extension Dictionary where Key: ExpressibleByStringLiteral, Value: AnyObject {

    var jsonString: String? {
    if let dict = (self as AnyObject) as? Dictionary<String, AnyObject> {
        do {
            let data = try JSONSerialization.data(withJSONObject: dict, options: JSONSerialization.WritingOptions(rawValue: UInt.allZeros))
            if let string = String(data: data, encoding: String.Encoding.utf8) {
                return string
            }
        } catch {
            print(error)
        }
    }
    return nil
    }

}

Where I write something like:

let x: [String: String] = ["": ""]    
x.jsonString

I get this error:

Value of type '[String: String]' as no member 'jsonString'

Anything I am missing?

`String` is a value type and doesn't conform to `AnyObject`. Try using `Any` instead. — vacawama, Aug 02 '18 at 21:14

score 3 · Accepted Answer · answered Aug 02 '18 at 22:34

3

There is no need to constrain Dictionary Value type at all:

extension Dictionary where Key: ExpressibleByStringLiteral {
    var jsonString: String? {
        guard let data = try? JSONSerialization.data(withJSONObject: self)
        else { return nil }
        return String(data: data, encoding: .utf8)
    }
}

answered Aug 02 '18 at 22:34

Leo Dabus

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Sorry, it doesn't work. Maybe it is related with Swift 4? – bashan Aug 03 '18 at 17:23
Doesn’t work it is too vague. I have tested it here with a dictionary [String:String] and it work as expected – Leo Dabus Aug 03 '18 at 18:11
Same error... not sure why I keep getting it... Maybe the file of the extension is somehow not recognized...? – bashan Aug 03 '18 at 20:12
Make sure your file is listed in the Compile Sources in your app targets build phases – Leo Dabus Aug 03 '18 at 20:15
The file is listed in Compile Sources, but it kept not working, so I copied the extension to another file with another working extension and it works. Strange thing... THANKS! – bashan Aug 04 '18 at 08:50

score 2 · Answer 2 · answered Aug 02 '18 at 21:35

Since String is a value type , look for it's

public struct String {

and AnyObject refers to any instance of a class only , and is equivalent to id in Objective-C , so this declaration of x

[String: String] doesn't fit with [String: AnyObject]

because Any refers to any instance of a class, struct, or enum so it'll fit perfectly

Dictionary extension in Swift is not recognized

2 Answers2