SwiftのCodableでEnumを変換する

import UIKit

enum Country: Int, Codable {
    case japan = 0
    case usa
    case france
}

struct Member: Codable {
    let id: Int
    let country: Country
}

let json = """
{
    "id": 1,
    "country": 0
}
"""

let decoded = try JSONDecoder().decode(Member.self, from: json.data(using: .utf8)!)
let country = decoded.country

switch country {
    case .japan:
        print("日本")
    case .usa:
        print("アメリカ")
    case .france:
        print("フランス")
}

print(decoded.country)

Swiftで文字列のJSONをStructのインスタンスに変換する。

import UIKit

protocol Json : Codable {
    func json(key: String) -> String!
    var json:String! { get }

}

extension Json {
    func json(key: String) -> String! {
        let encoder = JSONEncoder()
        encoder.dateEncodingStrategy = .iso8601
        encoder.outputFormatting = .prettyPrinted
        guard let data = try? encoder.encode([key : self]) else {
            return nil
        }
        return String(data: data, encoding: .utf8)!
    }
}

extension Json {
    var json: String! {
        let encoder = JSONEncoder()
        encoder.dateEncodingStrategy = .iso8601
        encoder.outputFormatting = .prettyPrinted
        guard let data = try? encoder.encode(self) else {
            return nil
        }
        return String(data: data, encoding: .utf8)!
    }
}

struct User: Json {
    let name: String
    let age: Int
}

struct Admin: Json {
    let user: User
    let permission: Int
}

let user = User(name: "田中", age: 9)
let admin = Admin(user: user, permission: 5)

var decoder = JSONDecoder()

extension String {
    func decode<T: Decodable>() -> T {
        return try! decoder.decode(T.self, from: self.data(using: .utf8)!)
    }
}

if let json = user.json {
    let user: User = json.decode()
    print(user.name)
    print(user.age)
}

構造体にjsonメソッドとjsonプロパティを拡張すると便利？？？？

import UIKit

protocol Json : Codable {
    func json(key: String) -> String!
    var json:String! { get }

}

extension Json {
    func json(key: String) -> String! {
        let encoder = JSONEncoder()
        encoder.dateEncodingStrategy = .iso8601
        encoder.outputFormatting = .prettyPrinted
        guard let data = try? encoder.encode([key : self]) else {
            return nil
        }
        return String(data: data, encoding: .utf8)!
    }
}

extension Json {
    var json: String! {
        let encoder = JSONEncoder()
        encoder.dateEncodingStrategy = .iso8601
        encoder.outputFormatting = .prettyPrinted
        guard let data = try? encoder.encode(self) else {
            return nil
        }
        return String(data: data, encoding: .utf8)!
    }
}

struct User: Json {
    let name: String
    let age: Int
}

struct Admin: Json {
    let user: User
    let permission: Int
}

let user = User(name: "田中", age: 9)
let admin = Admin(user: user, permission: 5)

print(admin.json(key: "top") ?? "失敗")
print(admin.json ?? "top")