Decoding Result<A, E> types in swift

Decoding Result type.playground

//: Playground - noun: a place where people can play

import UIKit

let errorJsonData = """
{
"message": "The message",
"reference_url": "https://www.api.refer.co"
}
""".data(using: .utf8)!

let responseJSONData = """
{
"value" : {
"name": "DrStrangers",
"surname": "We dont have surnames",
"id": 2
}
}
""".data(using: .utf8)!


struct Object: Decodable {
    var name: String
    var surname: String
    var id: Int
}

struct ResponseError: Decodable, Error {
    var message: String
    var reference_url: String
}

enum Result<A> {
    case value(A)
    case error(Error)
    
    enum CodingKeys: String, CodingKey {
        case value
        case error
    }
}

extension Result: Decodable where A: Decodable {
    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        if let value = try container.decodeIfPresent(A.self, forKey: .value) {
            self = .value(value)
        } else {
            let errorContainer = try decoder.singleValueContainer()
            let error = try errorContainer.decode(ResponseError.self)
            self = .error(error)
        }
    }
}

do {
    let obj = try JSONDecoder().decode(Result<Object>.self, from: errorJsonData)
    dump(obj)
} catch {
    print(error)
}


// PRINTS

__lldb_expr_26.Result<__lldb_expr_26.Object>.error
  ▿ error: __lldb_expr_26.ResponseError
    - message: "The message"
    - reference_url: "https://www.api.refer.co"


do {
    let obj = try JSONDecoder().decode(Result<Object>.self, from: responseJSONData)
    dump(obj)
} catch {
    print(error)
}

// PRINTS
__lldb_expr_29.Result<__lldb_expr_29.Object>.value
  ▿ value: __lldb_expr_29.Object
    - name: "DrStrangers"
    - surname: "We dont have surnames"
    - id: 2