Merge pull request SqliteModernCpp#154 from zauguin/new_value_interface

Return values instead of assigning to references

Author: zauguin

hdr/sqlite_modern_cpp.h

@@ -135,11 +135,15 @@ namespace sqlite {
 			value_type(database_binder *_binder): _binder(_binder) {};
 			template<class T>
 			typename std::enable_if<is_sqlite_value<T>::value, value_type &>::type operator >>(T &result) {
-				get_col_from_db(_binder->_stmt.get(), next_index++, result);
+				result = get_col_from_db(_binder->_stmt.get(), next_index++, result_type<T>());
 				return *this;
 			}
 			template<class ...Types>
-			value_type &operator >>(std::tuple<Types...>& values);
+			value_type &operator >>(std::tuple<Types...>& values) {
+				values = handle_tuple<std::tuple<typename std::decay<Types>::type...>>(std::index_sequence_for<Types...>());
+				next_index += sizeof...(Types);
+				return *this;
+			}
 			template<class ...Types>
 			value_type &operator >>(std::tuple<Types...>&& values) {
 				return *this >> values;
@@ -154,6 +158,14 @@ namespace sqlite {
 				return sqlite3_column_count(_binder->_stmt.get()) >= next_index;
 			}
 		private:
+			template<class Tuple, std::size_t ...Index>
+			Tuple handle_tuple(std::index_sequence<Index...>) {
+				return Tuple(
+						get_col_from_db(
+							_binder->_stmt.get(),
+							next_index + Index,
+							result_type<typename std::tuple_element<Index, Tuple>::type>())...);
+			}
 			database_binder *_binder;
 			int next_index = 0;
 		};
@@ -198,27 +210,6 @@ namespace sqlite {
 		mutable value_type value{_binder}; // mutable, because `changing` the value is just reading it
 	};
 
-	namespace detail {
-		template<typename Tuple, int Element = 0, bool Last = (std::tuple_size<Tuple>::value == Element)> struct tuple_iterate {
-			static void iterate(Tuple& t, row_iterator::value_type& row) {
-				row >> std::get<Element>(t);
-				tuple_iterate<Tuple, Element + 1>::iterate(t, row);
-			}
-		};
-
-		template<typename Tuple, int Element> struct tuple_iterate<Tuple, Element, true> {
-			static void iterate(Tuple&, row_iterator::value_type&) {}
-		};
-	}
-
-	template<class ...Types>
-	row_iterator::value_type &row_iterator::value_type::operator >>(std::tuple<Types...>& values) {
-		assert(!next_index);
-		detail::tuple_iterate<std::tuple<Types...>>::iterate(values, *this);
-		next_index = sizeof...(Types) + 1;
-		return *this;
-	}
-
 	inline row_iterator database_binder::begin() {
 		return row_iterator(*this);
 	}
@@ -558,16 +549,20 @@ namespace sqlite {
 				sqlite3_value**  vals,
 				Values&&...      values
 		) {
-			typename std::remove_cv<
+			using arg_type = typename std::remove_cv<
 					typename std::remove_reference<
 							typename utility::function_traits<
 									typename Functions::first_type
 							>::template argument<sizeof...(Values)>
 					>::type
-			>::type value{};
-			get_val_from_db(vals[sizeof...(Values) - 1], value);
+			>::type;
 
-			step<Count, Functions>(db, count, vals, std::forward<Values>(values)..., std::move(value));
+			step<Count, Functions>(
+					db,
+					count,
+					vals,
+					std::forward<Values>(values)...,
+					get_val_from_db(vals[sizeof...(Values) - 1], result_type<arg_type>()));
 		}
 
 		template<
@@ -618,14 +613,18 @@ namespace sqlite {
 				sqlite3_value**  vals,
 				Values&&...      values
 		) {
-			typename std::remove_cv<
+			using arg_type = typename std::remove_cv<
 					typename std::remove_reference<
 							typename utility::function_traits<Function>::template argument<sizeof...(Values)>
 					>::type
-			>::type value{};
-			get_val_from_db(vals[sizeof...(Values)], value);
-
-			scalar<Count, Function>(db, count, vals, std::forward<Values>(values)..., std::move(value));
+			>::type;
+
+			scalar<Count, Function>(
+					db,
+					count,
+					vals,
+					std::forward<Values>(values)...,
+					get_val_from_db(vals[sizeof...(Values)], result_type<arg_type>()));
 		}
 
 		template<