1. C++ / Говнокод #27307

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    namespace detail {
        template<entity_event_t Event>
        struct EventHasEntityStateConstructor {
            // Sanity check
            static_assert(static_cast<int32_t>(Event) >= 0
                          && static_cast<int32_t>(Event) < ENTITY_EVENTS_COUNT);
    
        private:
            struct TwoChar {
                char a, b;
            };
    
            template<typename T>
            constexpr static TwoChar _check(
                decltype(
                    T(std::declval<const entityState_t &>())
                )*
            );
    
            template<typename T>
            constexpr static char _check(...);
    
        public:
            constexpr inline static bool value = (sizeof(_check<EntityEvent<Event>>(nullptr)) == sizeof(TwoChar));
        };
    
        template<typename BusT, entity_event_t Event>
        bool defaultEntityEventPublisher(const BusT & bus, const entityState_t & eventEntity)
        {
            static_assert(EventHasEntityStateConstructor<Event>::value,
                          "defaultEntityEventFactory<Event>() instantiated for a custom\n"
                          "event that does not have a (const entityState_t & eventEntity) constructor.\n"
                          "This should not happen (you'll get a more obscured compiler error anyway)!");
            return bus.publishEmplace<EntityEvent<Event>>(eventEntity);
        }
    
        template<typename BusT, typename T, T... Is>
        constexpr std::array<EntityEventPublisherPtr<BusT>, sizeof...(Is)>
            createDefaultEntityEventFactories(std::integer_sequence<T, Is...>)
        {
            return {
                [](auto i) -> EntityEventPublisherPtr<BusT> {
                    if constexpr (EventHasEntityStateConstructor<static_cast<entity_event_t>(i.value)>::value) {
                        return &defaultEntityEventPublisher<BusT, static_cast<entity_event_t>(i.value)>;
                    } else {
                        return nullptr;
                    }
                }(std::integral_constant<T, Is>{})...
            };
        }
    }
    
    // An (event_number -> EntityState<event_number> 'publishing factory' function) mapping;
    // if event N could not be constructed from a single entityState_t reference
    // then this table would contain nullptr at the index N
    template<typename BusT>
    const std::array<EntityEventPublisherPtr<BusT>, ENTITY_EVENTS_COUNT> & getDefaultEntityEventsPublishers() noexcept
    {
        static auto factories = detail::createDefaultEntityEventFactories<BusT>(std::make_integer_sequence<int32_t, ENTITY_EVENTS_COUNT>());
        return factories;
    }
    
    template<typename BusT>
    EntityEventPublisherPtr<BusT> tryGetDefaultEntityEventPublisher(entity_event_t event) noexcept
    {
        auto eventNum = static_cast<int32_t>(event);
        if (eventNum >= 0 && eventNum < ENTITY_EVENTS_COUNT) {
            return getDefaultEntityEventsPublishers<BusT>()[eventNum];
        } else {
            return nullptr;
        }
    }

    Запостил: PolinaAksenova, 21 Марта 2021

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