User_Codable_v1.swift

struct User {
	typealias Id = String
	
	let id: Id
	let cellNumber: CellNumber
	let status: Status
	
	enum Status {
		case notRegistered
		case registered(profile: Profile)
	}
}

extension User: Codable {
	private enum CodingKeys: String, CodingKey {
		case id
		case cellNumber = "cell_number"
		case isRegistered = "is_registered"
		case profile
	}
	
	init(from decoder: Decoder) throws {
		let container = try decoder.container(keyedBy: CodingKeys.self)
		id = try container.decode(Id.self, forKey: .id) // notice Id.self instead of String.self
		cellNumber = try container.decode(CellNumber.self, forKey: .cellNumber)
		let isRegistered = try container.decode(Bool.self, forKey: .isRegistered)
		status = isRegistered ? try .registered(profile: container.decode(Profile.self, forKey: .profile)) : .notRegistered
	}
	
	func encode(to encoder: Encoder) throws {
		var container = encoder.container(keyedBy: CodingKeys.self)
		try container.encode(id, forKey: .id)
		try container.encode(cellNumber, forKey: .cellNumber)
		switch status {
		case .notRegistered:
			try container.encode(false, forKey: .isRegistered)
		case .registered(let profile):
			try container.encode(true, forKey: .isRegistered)
			try container.encode(profile, forKey: .profile)
		}
	}
}