Decode.swift

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

import Foundation

let userPayload = """
{
"id": 1337,
"username": "Palleas"
}
""".data(using: .utf8)!

struct ID: Decodable {
    let raw: Int

    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        self.raw = try container.decode(Int.self)
    }
}

struct User: Decodable {
    let id: ID
    let username: String
}

let decoder = JSONDecoder()
let u = try! decoder.decode(User.self, from: userPayload)
print("Username = \(u.username)")
print("User #\(u.id)")