how to use Codable with Class enum - swift

Question

I feel like I'm going way too far for what should really be a simple thing. With the below code, the error that I get is: Cannot invoke 'decode' with an argument list of type '(GameOfLife.Cell, forKey: GameOfLife.Cell.CodingKeys)'
extension GameOfLife {
enum Cell: Equatable, Codable {
case alive
case born
case dying
case dead
var isAlive: Bool {
switch self {
case .alive, .born: return true
case .dying, .dead: return false
}
}
var isDead: Bool {
switch self {
case .alive, .born: return false
case .dying, .dead: return true
}
}
func equalTo(_ rhs: Cell) -> Bool {
switch (self) {
case .alive, .born:
return rhs.isAlive
case .dead, .dying:
return rhs.isDead
}
}
init(_ living: Bool) {
self = living ? .alive : .dead
}
enum CodingKeys: CodingKey {
case alive
case born
case dying
case dead
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
do {
let leftValue = try container.decode(GameOfLife.Cell.alive, forKey: CodingKeys.alive)
self = GameOfLife.Cell.alive
} catch {
let leftValue = try container.decode(GameOfLife.Cell.born, forKey: CodingKeys.born)
self = GameOfLife.Cell.born
} catch {
let leftValue = try container.decode(GameOfLife.Cell.dying, forKey: CodingKeys.dying)
self = GameOfLife.Cell.dying
} catch {
let leftValue = try container.decode(GameOfLife.Cell.dead, forKey: CodingKeys.dead)
self = GameOfLife.Cell.dead
}
}
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
switch self {
case .alive:
try container.encode("alive", forKey: .alive)
case .born:
try container.encode("born", forKey: .born)
case .dying:
try container.encode("dying", forKey: .dying)
case .dead:
try container.encode("dead", forKey: .dead)
}
}
}
}

Answer 1

The first parameter of decode( is the expected type of the decoded object. As you are encoding the enum cases a String, it's supposed to be String
let leftValue = try container.decode(String.self, forKey: .alive) // The compiler can infer the type `CodingKeys`
However the entire init(from method makes no sense. If an error occurs inside a catch expression it is not going to be caught in the subsequent catch expression.
To encode an enum case as String just declare the raw type of the enum as String and delete the CodingKeys and the init(from and encode(to methods. And if you want to adopt Equatable you have to implement ==
extension GameOfLife : Codable {
enum Cell: String, Equatable, Codable {
case alive, born, dying, dead
var isAlive: Bool {
switch self {
case .alive, .born: return true
case .dying, .dead: return false
}
}
// isDead can be simplified
var isDead: Bool {
return !isAlive
}
static func == (lhs: Cell, rhs: Cell) -> Bool {
switch (lhs.isAlive, rhs.isAlive) {
case (true, true), (false, false): return true
default: return false
}
}
init(_ living: Bool) {
self = living ? .alive : .dead
}
}
}