Encode and decode an enum with associated types.

Barcode2.swift

// Accompanying blog post: http://127.0.0.1:4000/2017/07/11/encoding-and-decoding-custom-enums-with-associated-values-in-swift-4
// Also: https://gist.github.com/proxpero/189a723fb96bb88fac5bf9e11d6cf9e2
enum Barcode {
    case upc(Int, Int, Int, Int)
    case qrCode(String)
}

extension Barcode: Codable {

    private enum CodingKeys: String, CodingKey {
        case upc
        case qrCode
    }

    enum CodingError: Error {
        case decoding(String)
    }

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        if let codes = try? values.decode(Array<Int>.self, forKey: .upc), codes.count == 4 {
            self = .upc(codes[0], codes[1], codes[2], codes[3])
            return
        }

        if let code = try? values.decode(String.self, forKey: .qrCode) {
            self = .qrCode(code)
            return
        }

        throw CodingError.decoding("Decoding Error: \(dump(values))")
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        switch self {
        case .upc(let numberSystem, let manufacturer, let product, let check):
            try container.encode([numberSystem, manufacturer, product, check], forKey: .upc)
        case .qrCode(let productCode):
            try container.encode(productCode, forKey: .qrCode)
        }
    }
}


import Foundation

let encoder = JSONEncoder()
encoder.outputFormatting = .prettyPrinted
let decoder = JSONDecoder()
var productBarcode: Barcode
var data: Data
var json: String
var expectation: String
var result: Barcode

productBarcode = .upc(8, 85909, 51226, 3)
data = try encoder.encode(productBarcode)
json = String.init(data: data, encoding: .utf8)!
expectation = """
{
  "upc" : [
    8,
    85909,
    51226,
    3
  ]
}
"""
print(json)
result = try decoder.decode(Barcode.self, from: data)
//assert(result == productBarcode)


productBarcode = .qrCode("ABCDEFGHIJKLMNOP")
data = try encoder.encode(productBarcode)
json = String.init(data: data, encoding: .utf8)!
expectation = """
{
  "qrCode" : "ABCDEFGHIJKLMNOP"
}
"""
result = try decoder.decode(Barcode.self, from: data)
assert(json == expectation)
////assert(result == productBarcode)