func serialize(object: Any) -> [String : Any]? {
    let mirror = Mirror(reflecting: object)
    guard mirror.displayStyle == .struct || mirror.displayStyle == .class else {
        return .none
    }

    var result: [String : Any] = [:]
    for case let (label?, value) in mirror.children {
        let childMirror = Mirror(reflecting: value)
        if let displayStyle = childMirror.displayStyle {
            switch displayStyle {
            case .`class`:
                result[label] = serialize(object: value)
            case .collection:
                result[label] = Array(childMirror.children.lazy
                    .map { (_, value) in serialize(object: value) }
                    .filter { $0 != nil }
                    .map { $0 as! [String : Any]})
            case .dictionary:
                result[label] = serialize(object: value)
            case .`enum`:
                // not supported
                break
            case .optional:
                switch childMirror.children.first {
                case let .some((.some("some"), childValue)):
                    result[label] = serialize(object: childValue) ?? childValue
                default:
                    result[label] = NSNull()
                }
                break
            case .set:
                result[label] = Array(childMirror.children.lazy
                    .map { (_, value) in serialize(object: value) }
                    .filter { $0 != nil }
                    .map { $0 as! [String : String]})
            case .`struct`:
                result[label] = serialize(object: value)
            case .tuple:
                // not supported
                break
            }
        } else {
            result[label] = "\(value)"
        }
    }

    return result
}

let user = User(
    email: "guidomb@gmail.com",
    password: "asdasd",
    friends: [
        User(email: "anita@gmail.com", password: "123456"),
        User(email: "luciano@gmail.com", password: "asd123456")
    ]
)
print(serialize(object: user))