Replaced tag_yes and tag_no by std::true_type and std::false_type

include/sqlpp11/alias.h

@@ -87,9 +87,9 @@ namespace sqlpp
 	{
 		struct _value_type: Expression::_value_type
 		{
-			using _is_expression = tag_no;
+			using _is_expression = std::false_type;
-			using _is_named_expression = tag_yes;
+			using _is_named_expression = std::true_type;
-			using _is_alias = tag_yes;
+			using _is_alias = std::true_type;
 		};
 
 		using _name_t = typename AliasProvider::_name_t;

include/sqlpp11/any.h

@@ -42,7 +42,7 @@ namespace sqlpp
 
 			struct _value_type: public Select::_value_type::_base_value_type
 			{
-				using _is_named_expression = tag_yes;
+				using _is_named_expression = std::true_type;
 			};
 
 			struct _name_t

include/sqlpp11/assignment_list.h

@@ -50,7 +50,7 @@ namespace sqlpp
 			using _prohibited_assignment_set = typename detail::make_set_if<ProhibitPredicate, typename Assignment::column_type...>::type;
 			static_assert(_prohibited_assignment_set::size::value == 0, "at least one assignment is prohibited by its column definition in set()");
 
-			using _is_assignment_list = tag_yes;
+			using _is_assignment_list = std::true_type;
 
 			template<typename Db>
 				void serialize(std::ostream& os, Db& db) const

include/sqlpp11/avg.h

@@ -41,7 +41,7 @@ namespace sqlpp
 
 			struct _value_type: public Expr::_value_type::_base_value_type
 			{
-				using _is_named_expression = tag_yes;
+				using _is_named_expression = std::true_type;
 			};
 
 			struct _name_t

include/sqlpp11/boolean.h

@@ -60,9 +60,9 @@ namespace sqlpp
 		struct boolean
 		{
 			using _base_value_type = boolean;
-			using _is_boolean = tag_yes;
+			using _is_boolean = std::true_type;
-			using _is_value = tag_yes;
+			using _is_value = std::true_type;
-			using _is_expression = tag_yes;
+			using _is_expression = std::true_type;
 
 			struct plus_
 			{

include/sqlpp11/column.h

@@ -44,9 +44,9 @@ namespace sqlpp
 		using _column_type = typename ColumnSpec::_column_type;
 		struct _value_type: ColumnSpec::_value_type
 		{
-			using _is_expression = tag_yes;
+			using _is_expression = std::true_type;
-			using _is_named_expression = tag_yes;
+			using _is_named_expression = std::true_type;
-			using _is_alias = tag_no;
+			using _is_alias = std::false_type;
 		};
 
 		using _name_t = typename ColumnSpec::_name_t;

include/sqlpp11/concat.h

@@ -44,7 +44,7 @@ namespace sqlpp
 
 			struct _value_type: public First::_value_type::_base_value_type
 			{
-				using _is_named_expression = tag_yes;
+				using _is_named_expression = std::true_type;
 			};
 
 			struct _name_t

include/sqlpp11/count.h

@@ -41,7 +41,7 @@ namespace sqlpp
 
 			struct _value_type: public numeric
 			{
-				using _is_named_expression = tag_yes;
+				using _is_named_expression = std::true_type;
 			};
 
 			struct _name_t

include/sqlpp11/detail/tag.h

@@ -1,40 +0,0 @@
-/*
- * Copyright (c) 2013, Roland Bock
- * All rights reserved.
- * 
- * Redistribution and use in source and binary forms, with or without modification,
- * are permitted provided that the following conditions are met:
- * 
- *   Redistributions of source code must retain the above copyright notice, this
- *   list of conditions and the following disclaimer.
- * 
- *   Redistributions in binary form must reproduce the above copyright notice, this
- *   list of conditions and the following disclaimer in the documentation and/or
- *   other materials provided with the distribution.
- * 
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
- * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
- * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
- * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
- * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
- * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
- * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
- * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- */
-
-#ifndef SQLPP_DETAIL_TAG_H
-#define SQLPP_DETAIL_TAG_H
-
-namespace sqlpp
-{
-	namespace detail
-	{
-		struct tag {};
-	}
-	using tag_yes = detail::tag;
-	using tag_no = void;
-}
-
-#endif

include/sqlpp11/exists.h

@@ -41,7 +41,7 @@ namespace sqlpp
 
 			struct _value_type: public boolean
 			{
-				using _is_named_expression = tag_yes;
+				using _is_named_expression = std::true_type;
 			};
 
 			struct _name_t

include/sqlpp11/expression.h

@@ -37,7 +37,7 @@ namespace sqlpp
 	template<typename Lhs, typename Rhs>
 		struct assignment_t
 		{
-			using _is_assignment = tag_yes;
+			using _is_assignment = std::true_type;
 			using column_type = Lhs;
 			using value_type = Rhs;
 

include/sqlpp11/from.h

@@ -39,7 +39,7 @@ namespace sqlpp
 	template<typename... TableOrJoin>
 		struct from_t
 		{
-			using _is_from = tag_yes;
+			using _is_from = std::true_type;
 
 			// ensure one argument at least
 			static_assert(sizeof...(TableOrJoin), "at least one table or join argument required in from");
@@ -67,8 +67,8 @@ namespace sqlpp
 	template<typename Db>
 	struct dynamic_from_t
 	{
-		using _is_from = tag_yes;
+		using _is_from = std::true_type;
-		using _is_dynamic = tag_yes;
+		using _is_dynamic = std::true_type;
 
 		template<typename Table>
 		void add(Table&& table)

include/sqlpp11/group_by.h

@@ -52,7 +52,7 @@ namespace sqlpp
 			using _valid_expressions = typename detail::make_set_if<is_expression_t, Expr...>::type;
 			static_assert(_valid_expressions::size::value == sizeof...(Expr), "at least one argument is not an expression in group_by()");
 
-			using _is_group_by = tag_yes;
+			using _is_group_by = std::true_type;
 
 			template<typename Db>
 				void serialize(std::ostream& os, Db& db) const
@@ -68,8 +68,8 @@ namespace sqlpp
 	template<typename Db>
 		struct dynamic_group_by_t
 		{
-			using _is_group_by = tag_yes;
+			using _is_group_by = std::true_type;
-			using _is_dynamic = tag_yes;
+			using _is_dynamic = std::true_type;
 
 			template<typename Expr>
 				void add(Expr&& expr)

include/sqlpp11/having.h

@@ -41,7 +41,7 @@ namespace sqlpp
 		{
 			static_assert(is_expression_t<Expr>::value, "invalid expression argument in having()");
 
-			using _is_having = tag_yes;
+			using _is_having = std::true_type;
 
 			template<typename Db>
 				void serialize(std::ostream& os, Db& db) const
@@ -57,8 +57,8 @@ namespace sqlpp
 	struct dynamic_having_t
 	{
 
-		using _is_having = tag_yes;
+		using _is_having = std::true_type;
-		using _is_dynamic = tag_yes;
+		using _is_dynamic = std::true_type;
 
 		template<typename Expr>
 			void add(Expr&& expr)

include/sqlpp11/insert_list.h

@@ -64,7 +64,7 @@ namespace sqlpp
 			using _prohibited_assignment_set = typename detail::make_set_if<ProhibitPredicate, typename Assignment::column_type...>::type;
 			static_assert(_prohibited_assignment_set::size::value == 0, "at least one assignment is prohibited by its column definition in set()");
 
-			using _is_insert_list = tag_yes;
+			using _is_insert_list = std::true_type;
 
 			insert_list_t(Assignment... assignment):
 				_columns({assignment._lhs}...),

include/sqlpp11/join.h

@@ -58,8 +58,8 @@ namespace sqlpp
 		static_assert(Lhs::_table_set::template is_disjunct_from<typename Rhs::_table_set>::value, "joined tables must not be identical");
 
 		using _is_table = typename std::conditional<is_noop<On>::value, 
-					tag_no, 
+					std::false_type, 
-					tag_yes>::type;
+					std::true_type>::type;
 		using _table_set = typename std::conditional<is_noop<On>::value, 
 					void, 
 					typename Lhs::_table_set::template join<typename Rhs::_table_set>::type>::type;

include/sqlpp11/like.h

@@ -45,7 +45,7 @@ namespace sqlpp
 
 			struct _value_type: public Operand::_value_type::_base_value_type
 			{
-				using _is_named_expression = tag_yes;
+				using _is_named_expression = std::true_type;
 			};
 
 			struct _name_t

include/sqlpp11/limit.h

@@ -35,7 +35,7 @@ namespace sqlpp
 {
 	struct limit_t
 	{
-		using _is_limit = tag_yes;
+		using _is_limit = std::true_type;
 
 		template<typename Db>
 			void serialize(std::ostream& os, Db& db) const
@@ -48,8 +48,8 @@ namespace sqlpp
 
 	struct dynamic_limit_t
 	{
-		using _is_limit = tag_yes;
+		using _is_limit = std::true_type;
-		using _is_dynamic = tag_yes;
+		using _is_dynamic = std::true_type;
 
 		dynamic_limit_t():
 			_limit(0)

include/sqlpp11/max.h

@@ -41,7 +41,7 @@ namespace sqlpp
 
 			struct _value_type: public Expr::_value_type::_base_value_type
 			{
-				using _is_named_expression = tag_yes;
+				using _is_named_expression = std::true_type;
 			};
 
 			struct _name_t

include/sqlpp11/min.h

@@ -41,7 +41,7 @@ namespace sqlpp
 
 			struct _value_type: public Expr::_value_type::_base_value_type
 			{
-				using _is_named_expression = tag_yes;
+				using _is_named_expression = std::true_type;
 			};
 
 			struct _name_t

include/sqlpp11/multi_column.h

@@ -48,9 +48,9 @@ namespace sqlpp
 
 			struct _value_type: public no_value_t
 			{
-				using _is_named_expression = tag_yes;
+				using _is_named_expression = std::true_type;
 			};
-			using _is_multi_column = tag_yes;
+			using _is_multi_column = std::true_type;
 
 			template<typename Db>
 				void serialize(std::ostream& os, Db& db) const

include/sqlpp11/numeric.h

@@ -42,9 +42,9 @@ namespace sqlpp
 		struct numeric
 		{
 			using _base_value_type = numeric;
-			using _is_numeric = tag_yes;
+			using _is_numeric = std::true_type;
-			using _is_value = tag_yes;
+			using _is_value = std::true_type;
-			using _is_expression = tag_yes;
+			using _is_expression = std::true_type;
 			
 			template<size_t index>
 			struct _result_entry_t

include/sqlpp11/offset.h

@@ -35,7 +35,7 @@ namespace sqlpp
 {
 	struct offset_t
 	{
-		using _is_offset = tag_yes;
+		using _is_offset = std::true_type;
 
 		template<typename Db>
 			void serialize(std::ostream& os, Db& db) const
@@ -48,8 +48,8 @@ namespace sqlpp
 
 	struct dynamic_offset_t
 	{
-		using _is_offset = tag_yes;
+		using _is_offset = std::true_type;
-		using _is_dynamic = tag_yes;
+		using _is_dynamic = std::true_type;
 
 		dynamic_offset_t():
 			_offset(0)

include/sqlpp11/order_by.h

@@ -49,7 +49,7 @@ namespace sqlpp
 			using _valid_expressions = typename detail::make_set_if<is_sort_order_t, OrderExpr...>::type;
 			static_assert(_valid_expressions::size::value == sizeof...(OrderExpr), "at least one argument is not a sort order expression in order_by()");
 
-			using _is_order_by = tag_yes;
+			using _is_order_by = std::true_type;
 
 			template<typename Db>
 				void serialize(std::ostream& os, Db& db) const
@@ -64,8 +64,8 @@ namespace sqlpp
 	template<typename Db>
 		struct dynamic_order_by_t
 		{
-			using _is_order_by = tag_yes;
+			using _is_order_by = std::true_type;
-			using _is_dynamic = tag_yes;
+			using _is_dynamic = std::true_type;
 
 			template<typename Expr>
 				void add(Expr&& expr)

include/sqlpp11/select.h

@@ -91,8 +91,8 @@ namespace sqlpp
 			static_assert(is_noop<Limit>::value or is_limit_t<Limit>::value, "invalid 'limit' arguments");
 			static_assert(is_noop<Offset>::value or is_offset_t<Offset>::value, "invalid 'offset' arguments");
 
-			using _is_select = tag_yes;
+			using _is_select = std::true_type;
-			using _requires_braces = tag_yes;
+			using _requires_braces = std::true_type;
 
 			template<typename FromT> 
 				using set_from_t = select_t<Database, Flags, ExpressionList, FromT, Where, GroupBy, Having, OrderBy, Limit, Offset>;

include/sqlpp11/select_expression_list.h

@@ -65,15 +65,15 @@ namespace sqlpp
 			static_assert(not detail::has_duplicates<typename NamedExpr::_name_t...>::value, "at least one duplicate name detected");
 			
 			// declare this to be a select expression
-			using _is_select_expression_list = tag_yes;
+			using _is_select_expression_list = std::true_type;
 
 			// provide type information for sub-selects that are used as expressions
 			struct _column_type {};
 			struct _value_type: std::conditional<sizeof...(NamedExpr) == 1, typename detail::get_first_argument<NamedExpr...>::type::_value_type, no_value_t>::type
 			{
-				using _is_expression = typename std::conditional<sizeof...(NamedExpr) == 1, tag_yes, tag_no>::type;
+				using _is_expression = typename std::conditional<sizeof...(NamedExpr) == 1, std::true_type, std::false_type>::type;
-				using _is_named_expression = typename std::conditional<sizeof...(NamedExpr) == 1, tag_yes, tag_no>::type;
+				using _is_named_expression = typename std::conditional<sizeof...(NamedExpr) == 1, std::true_type, std::false_type>::type;
-				using _is_alias = tag_no;
+				using _is_alias = std::false_type;
 			};
 			struct _no_name_t {};
 			using _name_t = typename std::conditional<sizeof...(NamedExpr) == 1, typename detail::get_first_argument<NamedExpr...>::type::_name_t, _no_name_t>::type;

include/sqlpp11/select_flag_list.h

@@ -41,7 +41,7 @@ namespace sqlpp
 	{
 		struct _value_type 
 		{ 
-			using _is_select_flag = tag_yes; 
+			using _is_select_flag = std::true_type; 
 		};
 
 		template<typename Db>
@@ -56,7 +56,7 @@ namespace sqlpp
 	{
 		struct _value_type 
 		{ 
-			using _is_select_flag = tag_yes; 
+			using _is_select_flag = std::true_type; 
 		};
 
 		template<typename Db>
@@ -71,7 +71,7 @@ namespace sqlpp
 	{
 		struct _value_type 
 		{ 
-			using _is_select_flag = tag_yes; 
+			using _is_select_flag = std::true_type; 
 		};
 
 		template<typename Db>
@@ -93,7 +93,7 @@ namespace sqlpp
 			using _valid_flags = typename detail::make_set_if<is_select_flag_t, Flag...>::type;
 			static_assert(_valid_flags::size::value == sizeof...(Flag), "at least one argument is not a select flag in select flag list");
 
-			using _is_select_flag_list = tag_yes; 
+			using _is_select_flag_list = std::true_type; 
 
 			template<typename Db>
 				void serialize(std::ostream& os, Db& db) const

include/sqlpp11/some.h

@@ -42,7 +42,7 @@ namespace sqlpp
 
 			struct _value_type: public Select::_value_type::_base_value_type
 			{
-				using _is_named_expression = tag_yes;
+				using _is_named_expression = std::true_type;
 			};
 
 			struct _name_t

include/sqlpp11/sort_order.h

@@ -38,7 +38,7 @@ namespace sqlpp
 	template<typename Expression, sort_type SortType>
 		struct sort_order_t
 		{
-			using _is_sort_order = tag_yes;
+			using _is_sort_order = std::true_type;
 
 			template<typename Db>
 				void serialize(std::ostream& os, Db& db) const

include/sqlpp11/sum.h

@@ -41,7 +41,7 @@ namespace sqlpp
 
 			struct _value_type: public Expr::_value_type::_base_value_type
 			{
-				using _is_named_expression = tag_yes;
+				using _is_named_expression = std::true_type;
 			};
 
 			struct _name_t

include/sqlpp11/table_base.h

@@ -46,7 +46,7 @@ namespace sqlpp
 		using _required_insert_columns = typename detail::make_set_if<require_insert_t, column_t<Table, ColumnSpec>...>::type;
 		using _all_of_t = std::tuple<column_t<Table, ColumnSpec>...>;
 
-		using _is_table = tag_yes;
+		using _is_table = std::true_type;
 
 		template<typename T>
 			join_t<inner_join_t, Table, typename std::decay<T>::type> join(T&& t)
@@ -57,14 +57,14 @@ namespace sqlpp
 		template<typename AliasProvider>
 			struct alias_t: public ColumnSpec::_name_t::template _member_t<column_t<AliasProvider, ColumnSpec>>...
 		{
-			using _is_table = tag_yes;
+			using _is_table = std::true_type;
 			using _table_set = detail::set<alias_t>;
 
 			struct _value_type: Table::_value_type
 			{
-				using _is_expression = tag_no;
+				using _is_expression = std::false_type;
 				using _is_named_expression = copy_type_trait<Table, is_value_t>;
-				using _is_alias = tag_yes;
+				using _is_alias = std::true_type;
 			};
 
 			using _name_t = typename AliasProvider::_name_t;

include/sqlpp11/text.h

@@ -43,9 +43,9 @@ namespace sqlpp
 		struct text
 		{
 			using _base_value_type = text;
-			using _is_text = tag_yes;
+			using _is_text = std::true_type;
-			using _is_value = tag_yes;
+			using _is_value = std::true_type;
-			using _is_expression = tag_yes;
+			using _is_expression = std::true_type;
 
 			template<size_t index>
 			struct _result_entry_t

include/sqlpp11/type_traits.h

@@ -27,8 +27,9 @@
 #ifndef SQLPP_TYPE_TRAITS_H
 #define SQLPP_TYPE_TRAITS_H
 
+#include <type_traits>
 #include <sqlpp11/detail/wrap_operand.h>
-#include <sqlpp11/detail/tag.h>
+
 namespace sqlpp
 {
 #define SQLPP_IS_VALUE_TRAIT_GENERATOR(name) \
@@ -37,7 +38,7 @@ namespace sqlpp
 		template<typename T, typename Enable = void>\
 			struct is_##name##_impl: std::false_type {};\
 		template<typename T>\
-			struct is_##name##_impl<T, typename std::enable_if<std::is_same<typename T::_value_type::_is_##name, tag>::value>::type>: std::true_type {};\
+			struct is_##name##_impl<T, typename std::enable_if<std::is_same<typename T::_value_type::_is_##name, std::true_type>::value>::type>: std::true_type {};\
 	}\
 	template<typename T>\
 		struct is_##name##_t: detail::is_##name##_impl<T> {};
@@ -48,7 +49,7 @@ namespace sqlpp
 		template<typename T, typename Enable = void>\
 			struct name##_impl: std::false_type {};\
 		template<typename T>\
-			struct name##_impl<T, typename std::enable_if<std::is_same<typename T::_column_type::_##name, tag>::value>::type>: std::true_type {};\
+			struct name##_impl<T, typename std::enable_if<std::is_same<typename T::_column_type::_##name, std::true_type>::value>::type>: std::true_type {};\
 	}\
 	template<typename T>\
 		struct name##_t: detail::name##_impl<T> {};
@@ -59,7 +60,7 @@ namespace sqlpp
 		template<typename T, typename Enable = void>\
 			struct name##_impl: std::false_type {};\
 		template<typename T>\
-			struct name##_impl<T, typename std::enable_if<std::is_same<typename T::_##name, tag>::value>::type>: std::true_type {};\
+			struct name##_impl<T, typename std::enable_if<std::is_same<typename T::_##name, std::true_type>::value>::type>: std::true_type {};\
 	}\
 	template<typename T>\
 		struct name##_t: detail::name##_impl<T> {};
@@ -70,7 +71,7 @@ namespace sqlpp
 		template<typename T, typename Enable = void>\
 			struct connector_##name##_impl: std::false_type {};\
 		template<typename T>\
-			struct connector_##name##_impl<T, typename std::enable_if<std::is_same<typename T::_tags::_##name, tag>::value>::type>: std::true_type {};\
+			struct connector_##name##_impl<T, typename std::enable_if<std::is_same<typename T::_tags::_##name, std::true_type>::value>::type>: std::true_type {};\
 	}\
 	template<typename T>\
 		struct connector_##name##_t: detail::connector_##name##_impl<T> {};
@@ -115,7 +116,7 @@ namespace sqlpp
 	SQLPP_CONNECTOR_TRAIT_GENERATOR(has_empty_list_insert);
 
 	template<typename T, template<typename> class IsTag>
-		using copy_type_trait = typename std::conditional<IsTag<T>::value, detail::tag, void>::type;
+		using copy_type_trait = typename std::conditional<IsTag<T>::value, std::true_type, std::false_type>::type;
 
 	template<typename T, template<typename> class IsCorrectType>
 		struct operand_t

include/sqlpp11/using.h

@@ -36,7 +36,7 @@ namespace sqlpp
 	template<typename... Table>
 		struct using_t
 		{
-			using _is_using = tag_yes;
+			using _is_using = std::true_type;
 
 			static_assert(sizeof...(Table), "at least one table argument required in using");
 

include/sqlpp11/where.h

@@ -42,7 +42,7 @@ namespace sqlpp
 		{
 			static_assert(is_expression_t<Expr>::value, "invalid expression argument in where()");
 
-			using _is_where = tag_yes;
+			using _is_where = std::true_type;
 
 			template<typename Db>
 				void serialize(std::ostream& os, Db& db) const
@@ -58,8 +58,8 @@ namespace sqlpp
 	struct dynamic_where_t
 	{
 
-		using _is_where = tag_yes;
+		using _is_where = std::true_type;
-		using _is_dynamic = tag_yes;
+		using _is_dynamic = std::true_type;
 
 		template<typename Expr>
 			void add(Expr&& expr)

tests/SelectTest.cpp

@@ -277,7 +277,7 @@ int main()
 	static_assert(sqlpp::is_select_flag_t<decltype(sqlpp::all)>::value, "sqlpp::all has to be a select_flag");
   using T = sqlpp::detail::wrap_operand<int>::type;
 	static_assert(T::_is_expression, "T has to be an expression");
-	static_assert(std::is_same<typename T::_value_type::_is_numeric, sqlpp::detail::tag>::value, "T has to be a numeric");
+	static_assert(std::is_same<typename T::_value_type::_is_numeric, std::true_type>::value, "T has to be a numeric");
 	static_assert(sqlpp::is_numeric_t<T>::value, "T has to be a numeric");
 	static_assert(sqlpp::is_numeric_t<decltype(t.alpha)>::value, "TabSample.alpha has to be a numeric");
 	((t.alpha + 7) + 4).asc();
@@ -291,7 +291,7 @@ int main()
 	static_assert(sqlpp::must_not_insert_t<decltype(t.alpha)>::value, "alpha must not be inserted");
 	t.alpha.serialize(std::cerr, db);
 	std::cerr << "\n" << sizeof(TabSample) << std::endl;
-	static_assert(std::is_same<typename decltype(t.alpha)::_value_type::_is_named_expression, sqlpp::detail::tag>::value, "alpha should be a named expression");
+	static_assert(std::is_same<typename decltype(t.alpha)::_value_type::_is_named_expression, std::true_type>::value, "alpha should be a named expression");
 	static_assert(sqlpp::is_named_expression_t<decltype(t.alpha)>::value, "alpha should be a named expression");
 	static_assert(sqlpp::is_named_expression_t<decltype(t.alpha.as(sqlpp::alias::a))>::value, "an alias of alpha should be a named expression");
 	static_assert(sqlpp::is_alias_t<decltype(t.alpha.as(sqlpp::alias::a))>::value, "an alias of alpha should be an alias");

tests/TabSample.h

@@ -89,10 +89,10 @@ namespace TabSample_
 		using _value_type = sqlpp::bigint;
 		struct _column_type
 		{
-			using _must_not_insert = sqlpp::tag_yes;
+			using _must_not_insert = std::true_type;
-			using _must_not_update = sqlpp::tag_yes;
+			using _must_not_update = std::true_type;
-			using _can_be_null = sqlpp::tag_yes;
+			using _can_be_null = std::true_type;
-			using _trivial_value_is_null = sqlpp::tag_yes;
+			using _trivial_value_is_null = std::true_type;
 			using _foreign_key = decltype(TabFoo::omega);
 		};
 	};
@@ -111,9 +111,9 @@ namespace TabSample_
 		using _value_type = sqlpp::varchar;
 		struct _column_type
 		{
-			using _can_be_null = sqlpp::tag_yes;
+			using _can_be_null = std::true_type;
-			using _trivial_value_is_null = sqlpp::tag_yes;
+			using _trivial_value_is_null = std::true_type;
-			using _must_not_update = sqlpp::tag_yes;
+			using _must_not_update = std::true_type;
 		};
 	};
 
@@ -131,7 +131,7 @@ namespace TabSample_
 		using _value_type = sqlpp::boolean;
 		struct _column_type
 		{
-			using _require_insert = sqlpp::tag_yes;
+			using _require_insert = std::true_type;
 		};
 	};
 }