cpp11chat/check_policy.hpp

#pragma once
#include <type_traits>
#include "chat_messages.hpp"



/* SFINAE compile-type checker for receive policies (as defined in chat_networking.hpp)
 * it checks whether PolicyCandidate supplies all of the following methods:
 *      - static void message_do_what(chat_message)
 *      - static void handshake_do_what(chat_message)
 *      - static void serverdirection_do_what(chat_message)
 *      - static void login_do_what(chat_message)
 *      - static void logout_do_what(chat_message)                                   */
template <class PolicyCandidate, typename = void>
struct is_valid_receive_policy : std::false_type {};

template <class PolicyCandidate>
struct is_valid_receive_policy<
        PolicyCandidate,
        typename
        std::enable_if<
                std::is_same<
                        decltype(PolicyCandidate
                                 ::message_do_what(std::declval<chat::chat_message>())),
                        void
                >::value
                &&
                std::is_same<
                        decltype(PolicyCandidate
                                 ::handshake_do_what(std::declval<chat::chat_message>())),
                        void
                >::value
                &&
                std::is_same<
                        decltype(PolicyCandidate
                                 ::serverdirection_do_what(std::declval<chat::chat_message>())),
                        void
                >::value
                &&
                std::is_same<
                        decltype(PolicyCandidate
                                 ::login_do_what(std::declval<chat::chat_message>())),
                        void
                >::value
                &&
                std::is_same<
                        decltype(PolicyCandidate
                                 ::logout_do_what(std::declval<chat::chat_message>())),
                        void
                >::value
        >::type>
: std::true_type {};


/* SFINAE compile-type checker for send policies (as defined in chat_networking.hpp)
 * it checks whether PolicyCandidate supplies all of the following methods:
 *      - static bool check_msg_length(chat_message)                              */
template <class PolicyCandidate, typename = void>
struct is_valid_send_policy : std::false_type {};

template <class PolicyCandidate>
struct is_valid_send_policy<
        PolicyCandidate,
        typename
        std::enable_if<
                std::is_same<
                        decltype(PolicyCandidate
                                 ::check_msg_length(std::declval<chat::chat_message>())),
                        bool
                >::value
        >::type>
: std::true_type {};