Mission Impossible / How to create datatypes which cannot contain invalid state

adrianimboden

18.4K views

01 Introduction

Introduction

02 Enums

Enums - Overview Enums - Hands On Enums - Example Solution

03 Optional

Optional - Overview Optional - Hands On Optional - Example Solution

04 Variant

Variant - Overview Variant - Hands On Variant - Example Solution

05 Final

Final - Hands On Final - Example Solution

Previous: Final - Hands On

Authentication Procedure

// {
#include <boost/assert.hpp>
#include <optional>
#include <set>
#include <string>
#include <variant>
// likely part of C++20
template <class... Ts>
struct overloaded : Ts... {
    using Ts::operator()...;
};
template <class... Ts>
overloaded(Ts...)->overloaded<Ts...>;
// }
// given
bool send_mail(std::string recipient, std::string token) {
    return true;
}
// end given
enum class UserLevel { logged_out, normal, admin };
struct AuthConfig {
    std::set<std::string> users;
    std::set<std::string> admins;
};
class AuthenticationProcedure {
private:
    struct LoggedOut {};
    struct TokenRequested {
        std::string token;
        std::string email;
    };
    struct LoggedIn {
        std::string email;
    };
    using State = std::variant<LoggedOut, TokenRequested, LoggedIn>;
public:
    struct VisibleState {
        UserLevel                  level;
        std::optional<std::string> email;
    };
    enum class LoginResult { success, failure };
    enum class RequestTokenResult { mail_sent, mail_send_error, not_authorized };
    explicit AuthenticationProcedure(AuthConfig config)