The JSONEncoder encode Dictionary to Array?

[Xezun]

struct Name: RawRepresentable, Codable, Hashable {
    typealias RawValue = String
    var rawValue: String
    init(rawValue: String) {
        self.rawValue = rawValue
    }
    var hashValue: Int {
        return rawValue.hashValue
    }
    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        let rawValue = try container.decode(String.self)
        self.init(rawValue: rawValue)
    }
    
    func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        try container.encode(rawValue)
    }
}

let value0 = Name.init(rawValue: "Name")
let encoder0 = JSONEncoder()
if let data = try? encoder0.encode(value0) {
    if let string = String(data: data, encoding: .utf8) {
        print(string) // ✅ prints: "Name"
    }
}

let value1 = [Name.init(rawValue: "Name"): "John"]
let encoder1 = JSONEncoder()
if let data = try? encoder1.encode(value1) {
    if let string = String(data: data, encoding: .utf8) {
        print(string) // ❌ prints: ["Name","John"]
    }
}

let value2 = ["Name": Name.init(rawValue: "John")]
let encoder2 = JSONEncoder()
if let data = try? encoder2.encode(value2) {
    if let string = String(data: data, encoding: .utf8) {
        print(string) // ✅ prints: {"Name":"John"}
    }
}

Environment

• Swift compiler version info
• Xcode version info Xcode 14.2 Build version 14C18
• Deployment target: iOS
• swift-driver version: 1.62.15 Apple Swift version 5.7.2 (swiftlang-5.7.2.135.5 clang-1400.0.29.51)

[AnthonyLatsis]

cc @parkera

[parkera]

We don’t have enough info when encoding the ”bad” example to know that Name will be encoded as a single value container with just a String and therefore is suitable for use as a key in a JSON dictionary (which is of course required to be a String). Therefore Dictionary goes into the fallback path of encoding itself as an Array instead.

[Xezun]

If a dictionary's key type is defined by OC like this:

typedef NSString *SomeKeyName NS_EXTENSIBLE_STRING_ENUM;

In swift, the key type was converted to struct, which lead to the JSONEncoder doesn't work as expected.

The JSONSerialization may work, but it needs all the value types implemented NSCoding protocol at first.

Is there any way to resolve this problem without changing many codes?

Thank you!

@parkera

[miku1958]

I had the same problem, my goal was to use a string enum as a key so that I could better process the results, but failed due to the lack of this feature. I believe When the Decoder thinks it's a Dictionary, it should be able to get the target type, and instead of decoding the key with String, it should decode it with Dictionary.Key, like the Dictionary.Value

[YOCKOW]

Isn't this a duplicate of SR-7788?
I think SE-0320 is a workaround for this.

[miku1958]

@YOCKOW I just fixed this in swift-foundation(FoundationPreview), but it looks like I should move it to swift-corelibs-foundation?

[miku1958]

SE-0320 is the workaround, adding CodingKeyRepresentable is working for me.