struct Person {
    let name: String
}

struct Group {
    let name: String
    let members: [Person]
}

extension Person: Marshaling {
    func marshaled() -> [String: Any] {
        return ["name": self.name]
    }
}

extension Group: Marshaling {
    func marshaled() -> [String: Any] {
        return [
            "name": name,
            "members": self.members.map { $0.marshaled() }
        ]
    }
}

extension Group: Marshaling {
    func marshaled() -> [String: Any] {
        return [
            "name": name,
            "members": self.members.marshaled()
        ]
    }
}