Determining column_list in a more generic way.

By finding the last parameter which is a return value.

include/sqlpp11/detail/get_last.h

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2013-2014, 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_GET_LAST_H
+#define SQLPP_DETAIL_GET_LAST_H
+
+#include <type_traits>
+
+namespace sqlpp
+{
+	namespace detail
+	{
+		template<template<typename> class Predicate, typename Default, typename... T>
+			struct get_last_if_impl;
+
+		template<template<typename> class Predicate, typename Default>
+			struct get_last_if_impl<Predicate, Default>
+			{
+				using type = Default;
+			};
+
+		template<template<typename> class Predicate, typename Default, typename T, typename... Rest>
+			struct get_last_if_impl<Predicate, Default, T, Rest...>
+			{
+				using rest = typename get_last_if_impl<Predicate, Default, Rest...>::type;
+				using type = typename std::conditional<std::is_same<rest, Default>::value and Predicate<T>::value,
+							T,
+							rest>::type;
+			};
+
+		template<template<typename> class Predicate, typename Default, typename... T>
+			using get_last_if = typename get_last_if_impl<Predicate, Default, T...>::type;
+	}
+}
+
+
+#endif

include/sqlpp11/select.h

@@ -48,6 +48,7 @@
 #include <sqlpp11/vendor/policy_update.h>
 
 #include <sqlpp11/detail/arg_selector.h>
+#include <sqlpp11/detail/get_last.h>
 
 namespace sqlpp
 {
@@ -135,18 +136,20 @@ namespace sqlpp
 					provided_tables_of<_from_t> // Hint: extra_tables_t is not used here because it is just a helper for dynamic .add_*() methods and should not change the structural integrity
 							>;
 
+				using _result_provider = detail::get_last_if<is_return_value_t, vendor::noop, FlagList, ColumnList, From, ExtraTables, Where, GroupBy, Having, OrderBy, Limit, Offset>;
+
 				// A select can be used as a pseudo table if
 				//   - at least one column is selected
 				//   - the select is complete (leaks no tables)
 				using _can_be_used_as_table = typename std::conditional<
-					is_select_column_list_t<_column_list_t>::value and _required_tables::size::value == 0,
+					is_select_column_list_t<_result_provider>::value and _required_tables::size::value == 0,
 					std::true_type,
 					std::false_type
 					>::type;
 
 				using _value_type = typename std::conditional<
 					detail::make_type_set_if_t<is_missing_t, FlagList, ColumnList, From, ExtraTables, Where, GroupBy, Having, OrderBy, Limit, Offset>::size::value == 0,
-					value_type_of<_column_list_t>,
+					value_type_of<_result_provider>,
 					no_value_t // if a required statement part is missing (columns in a select), then the statement cannot be used as a value
 						>::type;
 

include/sqlpp11/vendor/noop.h

@@ -35,7 +35,8 @@ namespace sqlpp
 	{
 		struct noop 
 		{
-			using is_noop = std::true_type;
+			using _traits = make_traits<no_value_t, ::sqlpp::tag::noop>;
+			using _recursive_traits = make_recursive_traits<>;
 		};
 
 		template<typename Context>