さまざまな温度単位のリテラルという題の構文なのですが、 template constexpr quantity temperature_cast(quantity const q) { return quantity(conversion_traits::convert(static_cast(q))); } conversion_traitsは構造体の型かともいますが、この構造体のRとSは構造体の中の計算で使用されていないのですが、どう考えたらいいですか？また、conversion_traitsの構造体は、 main関数ではどのように選択されますか？ ``` #include #include bool are_equal(double const d1, double const d2, double const epsilon = 0.001) { return std::fabs(d1 - d2) < epsilon; } namespace temperature { enum class scale { celsius, fahrenheit, kelvin }; template class quantity { const double amount; public: constexpr explicit quantity(double const a) : amount(a) {} explicit operator double() const { return amount; } }; template inline bool operator==(quantity const& lhs, quantity const& rhs) { return are_equal(static_cast(lhs), static_cast(rhs)); } template inline bool operator!=(quantity const& lhs, quantity const& rhs) { return !(lhs == rhs); } template inline bool operator< (quantity const& lhs, quantity const& rhs) { return static_cast(lhs) < static_cast(rhs); } template inline bool operator> (quantity const& lhs, quantity const& rhs) { return rhs < lhs; } template inline bool operator<=(quantity const& lhs, quantity const& rhs) { return !(lhs > rhs); } template inline bool operator>=(quantity const& lhs, quantity const& rhs) { return !(lhs < rhs); } template constexpr quantity operator+(quantity const& q1, quantity const& q2) { return quantity(static_cast(q1) + static_cast(q2)); } template constexpr quantity operator-(quantity const& q1, quantity const& q2) { return quantity(static_cast(q1) - static_cast(q2)); } template struct conversion_traits { static double convert(double const value) = delete; }; template <> struct conversion_traits { static double convert(double const value) { return value + 273.15; } }; template <> struct conversion_traits { static double convert(double const value) { return value - 273.15; } }; template <> struct conversion_traits { static double convert(double const value) { return (value * 9) / 5 + 32;; } }; template <> struct conversion_traits { static double convert(double const value) { return (value - 32) * 5 / 9; } }; template <> struct conversion_traits { static double convert(double const value) { return (value + 459.67) * 5 / 9; } }; template <> struct conversion_traits { static double convert(double const value) { return (value * 9) / 5 - 459.67; } }; template constexpr quantity temperature_cast(quantity const q) { return quantity(conversion_traits::convert(static_cast(q))); } namespace temperature_scale_literals { constexpr quantity operator "" _deg(long double const amount) { return quantity {static_cast(amount)}; } constexpr quantity operator "" _f(long double const amount) { return quantity {static_cast(amount)}; } constexpr quantity operator "" _k(long double const amount) { return quantity {static_cast(amount)}; } } } int main() { using namespace temperature; using namespace temperature_scale_literals; auto t1{ 36.5_deg }; auto t2{ 79.0_f }; auto t3{ 100.0_k }; { auto tf = temperature_cast(t1); auto tc = temperature_cast(tf); assert(t1 == tc); } { auto tk = temperature_cast(t1); auto tc = temperature_cast(tk); assert(t1 == tc); } { auto tc = temperature_cast(t2); auto tf = temperature_cast(tc); assert(t2 == tf); } { auto tk = temperature_cast(t2); auto tf = temperature_cast(tk); assert(t2 == tf); } { auto tc = temperature_cast(t3); auto tk = temperature_cast(tc); assert(t3 == tk); } { auto tf = temperature_cast(t3); auto tk = temperature_cast(tf); assert(t3 == tk); } } ```

	@@ -1,1 +1,1 @@
1	- 構造体とtemplateｎ関係
1	+ 構造体とtemplateの関係

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