Support named captures in C++17 mode (issue #96)

Author: Hana Dusíková

include/ctre/return_type.hpp

@@ -114,6 +114,9 @@ template <typename Head, typename... Tail> struct captures<Head, Tail...>: captu
 	}
 #if __cpp_nontype_template_parameter_class
 	template <ctll::fixed_string Name> CTRE_FORCE_INLINE static constexpr bool exists() noexcept {
+#else
+	template <const auto & Name> CTRE_FORCE_INLINE static constexpr bool exists() noexcept {
+#endif
 		if constexpr (std::is_same_v<typename Head::name, void>) {
 			return captures<Tail...>::template exists<Name>();
 		} else {
@@ -124,7 +127,6 @@ template <typename Head, typename... Tail> struct captures<Head, Tail...>: captu
 			}
 		}
 	}
-#endif
 	template <size_t id> CTRE_FORCE_INLINE constexpr auto & select() noexcept {
 		if constexpr (id == Head::get_id()) {
 			return head;
@@ -155,6 +157,9 @@ template <typename Head, typename... Tail> struct captures<Head, Tail...>: captu
 	}
 #if __cpp_nontype_template_parameter_class
 	template <ctll::fixed_string Name> CTRE_FORCE_INLINE constexpr auto & select() const noexcept {
+#else
+	template <const auto & Name> CTRE_FORCE_INLINE constexpr auto & select() const noexcept {
+#endif
 		if constexpr (std::is_same_v<typename Head::name, void>) {
 			return captures<Tail...>::template select<Name>();
 		} else {
@@ -165,7 +170,6 @@ template <typename Head, typename... Tail> struct captures<Head, Tail...>: captu
 			}
 		}
 	}
-#endif
 };
 
 template <> struct captures<> {
@@ -178,9 +182,11 @@ template <> struct captures<> {
 	}
 #if __cpp_nontype_template_parameter_class
 	template <ctll::fixed_string> CTRE_FORCE_INLINE static constexpr bool exists() noexcept {
+#else
+	template <const auto &> CTRE_FORCE_INLINE static constexpr bool exists() noexcept {
+#endif
 		return false;
 	}
-#endif
 	template <size_t> CTRE_FORCE_INLINE constexpr auto & select() const noexcept {
 		return capture_not_exists;
 	}
@@ -189,9 +195,11 @@ template <> struct captures<> {
 	}
 #if __cpp_nontype_template_parameter_class
 	template <ctll::fixed_string> CTRE_FORCE_INLINE constexpr auto & select() const noexcept {
+#else
+	template <const auto &> CTRE_FORCE_INLINE constexpr auto & select() const noexcept {
+#endif
 		return capture_not_exists;
 	}
-#endif
 };
 
 template <typename Iterator, typename... Captures> class regex_results {
@@ -213,6 +221,8 @@ template <typename Iterator, typename... Captures> class regex_results {
 	}
 #if __cpp_nontype_template_parameter_class
 	template <ctll::fixed_string Name, typename = std::enable_if_t<decltype(_captures)::template exists<Name>()>> CTRE_FORCE_INLINE constexpr auto get() const noexcept {
+#else
+	template <const auto & Name, typename = std::enable_if_t<decltype(_captures)::template exists<Name>()>> CTRE_FORCE_INLINE constexpr auto get() const noexcept {
 		return _captures.template select<Name>();
 	}
 #endif