How to encode a mixed-value-type dictionary to JSON in Swift 4.1

Question

The code below works in Xcode 9.2 (Swift 4.0) but gives an error in Xcode 9.3 (Swift 4.1).

let dict: [String: Any] = [
    "status_code": 5,
    "status_message": "message"
]

let data = try! JSONEncoder().encode(dict)
                           // ^  generic parameter 'T' could not be inferred

I've tried making the dictionary [String: Encodable], and using a typealias to both dictionary types, with the same results. Swift doesn't let you specify the type in a generic call, so that gives a compiler error. What should this look like in Swift 4.1?

Answer 1

Is Dictionary Encodable?

In Swift 4.1 a Dictionary<Key, Value> conforms to Encodable only if Key and Value are Encodable themselves.

Examples of Encodable(s) dictionaries

[String:Int]
[String:String]
[String:Double]

Example of non Encodable(s) dictionaries

[String:Any]
[String:UIView]

So, how can you solve your problem?

Struct

Using a model value is probably the best solution

struct Status: Codable {
    let statusCode: Int
    let statusMessage: String
}

let status = Status(statusCode: 45, statusMessage: "message")
let data = try? JSONEncoder().encode(status)