Swift 4 JSON Decodable simplest way to decode type change

Question

With Swift 4\'s Codable protocol there\'s a great level of under the hood date and data conversion strategies.

Given the JSON:

{
    \"name\": \"Bob\         


        

Answer 1

The options above only deal with the situation that the given field is always String. Many times I've met APIs where the output was once a string, other times number. So this is my suggestion to solve this. It is up to you to alter this to throw exception or set the decoded value to nil.

var json = """
{
"title": "Apple",
"id": "20"
}
""";
var jsonWithInt = """
{
"title": "Apple",
"id": 20
}
""";

struct DecodableNumberFromStringToo: Decodable {
    var value: T
    init(from decoder: Decoder) {
        print("Decoding")
        if let container = try? decoder.singleValueContainer() {
            if let val = try? container.decode(T.self) {
                value = val
                return
            }

            if let str = try? container.decode(String.self) {
                value = T.init(str) ?? T.zero
                return
            }

        }
        value = T.zero
    }
}


struct MyData: Decodable {
    let title: String
    let _id: DecodableNumberFromStringToo

    enum CodingKeys: String, CodingKey {
        case title, _id = "id"
    }

    var id: Int {
        return _id.value
    }
}

do {
    let parsedJson = try JSONDecoder().decode(MyData.self, from: json.data(using: .utf8)!)

    print(parsedJson.id)

} catch {
    print(error as? DecodingError)
}


do {
    let parsedJson = try JSONDecoder().decode(MyData.self, from: jsonWithInt.data(using: .utf8)!)

    print(parsedJson.id)

} catch {
    print(error as? DecodingError)
}