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Question

I am looking to create a subtraction operator to compare DayTime classes that are in a Template class (TemplateDay). I can’t create a generic operator that would allow these classes to be compared with each other.

TemplateDay :

namespace db
{
template <const char *__entity_alias, const char *__entity_name>
    class TemplateDay : public IEntity, public IDay
    {
    public:
        class ID;
        class DayTime;

    private:
        static const std::string _table_name;
        static const EntityAlias _entity_alias;
        static const EntityName _entity_name;

        std::shared_ptr<ID> _id;
        std::shared_ptr<DayTime> _day_time;

    public:
        ~TemplateDay() = default;

        static const std::string &table_name();
        static const IEntityAlias &alias();
        static const EntityName &entity_name();

        template <class Attribute>
        inline TemplateDay &withID(Attribute &&id);
        template <class Attribute>
        inline TemplateDay &withDayTime(Attribute &&day_time);

        void set_foreign_entity_by_alias(const IEntity &foreign_entity) override final;
        void set_attribute_by_column_name(const IAttribute &attribute) override final;

        const std::string &get_table_name() const override final;
        virtual const IEntityAlias &get_alias() const override;

        JsonObject toJson() const override final;

        virtual std::unique_ptr<IEntity> clone() const override;
    };
}

namespace db
{
    inline extern constexpr const char DAY_ENTITY_ALIAS[] = "d";
    inline extern constexpr const char DAY_ENTITY_NAME[] = "days";
    typedef TemplateDay<DAY_ENTITY_ALIAS, DAY_ENTITY_NAME> Day;

    inline extern constexpr const char DAY_BIRTHDAY_ENTITY_ALIAS[] = "bd";
    inline extern constexpr const char DAY_BIRTHDAY_ENTITY_NAME[] = "birthday";
    typedef TemplateDay<DAY_BIRTHDAY_ENTITY_ALIAS, DAY_BIRTHDAY_ENTITY_NAME> Birthday;

    inline extern constexpr const char DAY_LAST_UPDATE_ENTITY_ALIAS[] = "lud";
    inline extern constexpr const char DAY_LAST_UPDATE_ENTITY_NAME[] = "last_update";
    typedef TemplateDay<DAY_LAST_UPDATE_ENTITY_ALIAS, DAY_LAST_UPDATE_ENTITY_NAME> LastUpdate;

    inline extern constexpr const char DAY_CREATION_DAY_ENTITY_ALIAS[] = "cd";
    inline extern constexpr const char DAY_CREATION_DAY_ENTITY_NAME[] = "creation_day";
    typedef TemplateDay<DAY_CREATION_DAY_ENTITY_ALIAS, DAY_CREATION_DAY_ENTITY_NAME> CreationDay;

    inline extern constexpr const char DAY_MODIFICATION_DAY_ENTITY_ALIAS[] = "md";
    inline extern constexpr const char DAY_MODIFICATION_DAY_ENTITY_NAME[] = "modification_day";
    typedef TemplateDay<DAY_MODIFICATION_DAY_ENTITY_ALIAS, DAY_MODIFICATION_DAY_ENTITY_NAME> ModificationDay;

    inline extern constexpr const char DAY_SEARCH_DAY_ENTITY_ALIAS[] = "sd";
    inline extern constexpr const char DAY_SEARCH_DAY_ENTITY_NAME[] = "search_day";
    typedef TemplateDay<DAY_SEARCH_DAY_ENTITY_ALIAS, DAY_SEARCH_DAY_ENTITY_NAME> SearchDay;

    inline extern constexpr const char DAY_LAST_PAID_DAY_ENTITY_ALIAS[] = "lpd";
    inline extern constexpr const char DAY_LAST_PAID_DAY_ENTITY_NAME[] = "last_paid_day";
    typedef TemplateDay<DAY_LAST_PAID_DAY_ENTITY_ALIAS, DAY_LAST_PAID_DAY_ENTITY_NAME> LastPaidDay;

    inline extern constexpr const char DAY_ACCOUNT_OPENED_ENTITY_ALIAS[] = "dao";
    inline extern constexpr const char DAY_ACCOUNT_OPENED_ENTITY_NAME[] = "day_account_opened";
    typedef TemplateDay<DAY_ACCOUNT_OPENED_ENTITY_ALIAS, DAY_ACCOUNT_OPENED_ENTITY_NAME> DayAccountOpened;

    inline extern constexpr const char DAY_SCORE_DAY_ENTITY_ALIAS[] = "sd2";
    inline extern constexpr const char DAY_SCORE_DAY_ENTITY_NAME[] = "score_day";
    typedef TemplateDay<DAY_SCORE_DAY_ENTITY_ALIAS, DAY_SCORE_DAY_ENTITY_NAME> ScoreDay;
}
}

Daytime :

template <const char *__entity_alias, const char *__entity_name>
    class TemplateDay<__entity_alias, __entity_name>::DayTime : public AAttribute, public IUniqueAttribute

This is what I tried :

namespace db
{
template <const char *__entity_alias_rhs, const char *__entity_name_rhs,
              const char *__entity_alias_lhs, const char *__entity_name_lhs>
    int operator-(const typename TemplateDay<__entity_alias_rhs, __entity_name_rhs>::DayTime &lhs,
                  const typename TemplateDay<__entity_alias_lhs, __entity_name_lhs>::DayTime &rhs) noexcept
    {
        const std::string &str_lhs = lhs.toString();
        const std::string &str_rhs = rhs.toString();

        int year_s[2] = {(std::atoi(str_lhs.substr(0, 4).c_str()) - 1900) * 365,
                         (std::atoi(str_rhs.substr(0, 4).c_str()) - 1900) * 365};

        int mon_s[2] = {std::atoi(str_lhs.substr(5, 2).c_str()) * 30,
                        std::atoi(str_rhs.substr(5, 2).c_str()) * 30};

        int day_s[2] = {std::atoi(str_lhs.substr(8).c_str()),
                        std::atoi(str_rhs.substr(8).c_str())};

        return (year_s[0] - year_s[1]) + (mon_s[0] - mon_s[1]) + (day_s[0] - day_s[1]);
    }
}

And here is my compilation error:

error: no match for ‘operator-’ (operand types are ‘const db::TemplateDay<(& db::DAY_CREATION_DAY_ENTITY_ALIAS), (& db::DAY_CREATION_DAY_ENTITY_NAME)>::DayTime’ and ‘const db::TemplateDay<(& db::DAY_CREATION_DAY_ENTITY_ALIAS), (& db::DAY_CREATION_DAY_ENTITY_NAME)>::DayTime’)
  152 |         const int interval = current_day - creation_day;
      |                              ~~~~~~~~~~~ ^ ~~~~~~~~~~~~
      |                              |             |
      |                              |             DayTime<[...],[...]>
      |                              DayTime<[...],[...]>

note:candidate: ‘template<const char* __entity_alias_rhs, const char* __entity_name_rhs, const char* __entity_alias_lhs, const char* __entity_name_lhs> int db::operator-(const typename db::TemplateDay<__entity_alias_rhs, __entity_name_rhs>::DayTime&, const typename db::TemplateDay<__entity_alias_lhs, __entity_name_lhs>::DayTime&)’
  157 |     int operator-(const typename TemplateDay<__entity_alias_rhs, __entity_name_rhs>::DayTime &lhs,

note:  template argument deduction/substitution failed:

note:   couldn’t deduce template parameter ‘__entity_alias_rhs’
  152 |         const int interval = current_day - creation_day;

If anyone knows how to fix this, it would be greatly appreciated! I feel like I’ve tried everything.

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Danh mục

C++ couldn’t deduce template parameter on subtraction operator