From 2c23769cdfc52c6b4d8da357af5f9168bc7d1fd6 Mon Sep 17 00:00:00 2001
From: rbock <rbock@eudoxos.de>
Date: Mon, 25 Aug 2014 08:43:42 +0200
Subject: [PATCH] Moved operator and parameter templates out of value classes,
 added member template

These templates are nicer when used.
---
 include/sqlpp11/avg.h                        |   5 +-
 include/sqlpp11/basic_expression_operators.h |  59 ++--
 include/sqlpp11/boolean.h                    |  79 +++--
 include/sqlpp11/boolean_expression.h         |   2 +-
 include/sqlpp11/column.h                     |   7 +-
 include/sqlpp11/concat.h                     |   5 +-
 include/sqlpp11/count.h                      |   5 +-
 include/sqlpp11/exists.h                     |   5 +-
 include/sqlpp11/expression.h                 |  25 +-
 include/sqlpp11/floating_point.h             | 138 ++++----
 include/sqlpp11/in.h                         |   5 +-
 include/sqlpp11/integral.h                   | 341 ++++++++++---------
 include/sqlpp11/is_null.h                    |   5 +-
 include/sqlpp11/like.h                       |   5 +-
 include/sqlpp11/max.h                        |   5 +-
 include/sqlpp11/min.h                        |   5 +-
 include/sqlpp11/no_value.h                   |  26 +-
 include/sqlpp11/parameter.h                  |   5 +-
 include/sqlpp11/statement.h                  |   2 +-
 include/sqlpp11/sum.h                        |   5 +-
 include/sqlpp11/table.h                      |   5 +-
 include/sqlpp11/text.h                       |  80 ++---
 include/sqlpp11/type_traits.h                |   3 +
 include/sqlpp11/value_type_fwd.h             |  65 ++++
 include/sqlpp11/verbatim.h                   |   5 +-
 tests/PreparedTest.cpp                       |  12 +-
 26 files changed, 509 insertions(+), 395 deletions(-)
 create mode 100644 include/sqlpp11/value_type_fwd.h

diff --git a/include/sqlpp11/avg.h b/include/sqlpp11/avg.h
index 8e3baaf5..27a61bcf 100644
--- a/include/sqlpp11/avg.h
+++ b/include/sqlpp11/avg.h
@@ -32,8 +32,9 @@
 namespace sqlpp
 {
 	template<typename Flag, typename Expr>
-		struct avg_t: public floating_point::template expression_operators<avg_t<Flag, Expr>>,
-		public alias_operators<avg_t<Flag, Expr>>
+		struct avg_t:
+			public expression_operators<avg_t<Flag, Expr>, floating_point>,
+			public alias_operators<avg_t<Flag, Expr>>
 	{
 		using _traits = make_traits<floating_point, ::sqlpp::tag::is_expression, ::sqlpp::tag::is_named_expression>;
 		using _recursive_traits = make_recursive_traits<Expr>;
diff --git a/include/sqlpp11/basic_expression_operators.h b/include/sqlpp11/basic_expression_operators.h
index 7c7d3ec8..e3bfb5e4 100644
--- a/include/sqlpp11/basic_expression_operators.h
+++ b/include/sqlpp11/basic_expression_operators.h
@@ -27,6 +27,7 @@
 #ifndef SQLPP_DETAIL_BASIC_EXPRESSION_OPERATORS_H
 #define SQLPP_DETAIL_BASIC_EXPRESSION_OPERATORS_H
 
+#include <sqlpp11/value_type_fwd.h>
 #include <sqlpp11/alias.h>
 #include <sqlpp11/sort_order.h>
 #include <sqlpp11/expression_fwd.h>
@@ -38,7 +39,7 @@
 namespace sqlpp
 {
 	// basic operators
-	template<typename Base, template<typename> class IsCorrectValueType>
+	template<typename Expr, typename ValueType>
 		struct basic_expression_operators
 		{
 			template<typename T>
@@ -47,107 +48,107 @@ namespace sqlpp
 					static constexpr bool value = 
 						(is_expression_t<T>::value // expressions are OK
 						 or is_multi_expression_t<T>::value) // multi-expressions like ANY are OK for comparisons, too
-						and IsCorrectValueType<T>::value // the correct value type is required, of course
+						and ValueType::template _is_valid_operand<T>::value // the correct value type is required, of course
 						;
 				};
 
 			template<typename T>
-				equal_to_t<Base, wrap_operand_t<T>> operator==(T t) const
+				equal_to_t<Expr, wrap_operand_t<T>> operator==(T t) const
 				{
 					using rhs = wrap_operand_t<T>;
 					static_assert(_is_valid_comparison_operand<rhs>::value, "invalid rhs operand in comparison");
 
-					return { *static_cast<const Base*>(this), {rhs{t}} };
+					return { *static_cast<const Expr*>(this), {rhs{t}} };
 				}
 
 			template<typename T>
-				not_equal_to_t<Base, wrap_operand_t<T>> operator!=(T t) const
+				not_equal_to_t<Expr, wrap_operand_t<T>> operator!=(T t) const
 				{
 					using rhs = wrap_operand_t<T>;
 					static_assert(_is_valid_comparison_operand<rhs>::value, "invalid rhs operand in comparison");
 
-					return { *static_cast<const Base*>(this), {rhs{t}} };
+					return { *static_cast<const Expr*>(this), {rhs{t}} };
 				}
 
 			template<typename T>
-				less_than_t<Base, wrap_operand_t<T>> operator<(T t) const
+				less_than_t<Expr, wrap_operand_t<T>> operator<(T t) const
 				{
 					using rhs = wrap_operand_t<T>;
 					static_assert(_is_valid_comparison_operand<rhs>::value, "invalid rhs operand in comparison");
 
-					return { *static_cast<const Base*>(this), rhs{t} };
+					return { *static_cast<const Expr*>(this), rhs{t} };
 				}
 
 			template<typename T>
-				less_equal_t<Base, wrap_operand_t<T>> operator<=(T t) const
+				less_equal_t<Expr, wrap_operand_t<T>> operator<=(T t) const
 				{
 					using rhs = wrap_operand_t<T>;
 					static_assert(_is_valid_comparison_operand<rhs>::value, "invalid rhs operand in comparison");
 
-					return { *static_cast<const Base*>(this), rhs{t} };
+					return { *static_cast<const Expr*>(this), rhs{t} };
 				}
 
 			template<typename T>
-				greater_than_t<Base, wrap_operand_t<T>> operator>(T t) const
+				greater_than_t<Expr, wrap_operand_t<T>> operator>(T t) const
 				{
 					using rhs = wrap_operand_t<T>;
 					static_assert(_is_valid_comparison_operand<rhs>::value, "invalid rhs operand in comparison");
 
-					return { *static_cast<const Base*>(this), rhs{t} };
+					return { *static_cast<const Expr*>(this), rhs{t} };
 				}
 
 			template<typename T>
-				greater_equal_t<Base, wrap_operand_t<T>> operator>=(T t) const
+				greater_equal_t<Expr, wrap_operand_t<T>> operator>=(T t) const
 				{
 					using rhs = wrap_operand_t<T>;
 					static_assert(_is_valid_comparison_operand<rhs>::value, "invalid rhs operand in comparison");
 
-					return { *static_cast<const Base*>(this), rhs{t} };
+					return { *static_cast<const Expr*>(this), rhs{t} };
 				}
 
-			is_null_t<true, Base> is_null() const
+			is_null_t<true, Expr> is_null() const
 			{
-				return { *static_cast<const Base*>(this) };
+				return { *static_cast<const Expr*>(this) };
 			}
 
-			is_null_t<false, Base> is_not_null() const
+			is_null_t<false, Expr> is_not_null() const
 			{
-				return { *static_cast<const Base*>(this) };
+				return { *static_cast<const Expr*>(this) };
 			}
 
-			sort_order_t<Base, sort_type::asc> asc() const
+			sort_order_t<Expr, sort_type::asc> asc() const
 			{ 
-				return { *static_cast<const Base*>(this) };
+				return { *static_cast<const Expr*>(this) };
 			}
 
-			sort_order_t<Base, sort_type::desc> desc() const
+			sort_order_t<Expr, sort_type::desc> desc() const
 			{ 
-				return { *static_cast<const Base*>(this) };
+				return { *static_cast<const Expr*>(this) };
 			}
 
 			// Hint: use value_list wrapper for containers...
 			template<typename... T>
-				in_t<true, Base, wrap_operand_t<T>...> in(T... t) const
+				in_t<true, Expr, wrap_operand_t<T>...> in(T... t) const
 				{
 					static_assert(detail::all_t<_is_valid_comparison_operand<wrap_operand_t<T>>::value...>::value, "at least one operand of in() is not valid");
-					return { *static_cast<const Base*>(this), wrap_operand_t<T>{t}... };
+					return { *static_cast<const Expr*>(this), wrap_operand_t<T>{t}... };
 				}
 
 			template<typename... T>
-				in_t<false, Base, wrap_operand_t<T>...> not_in(T... t) const
+				in_t<false, Expr, wrap_operand_t<T>...> not_in(T... t) const
 				{
 					static_assert(detail::all_t<_is_valid_comparison_operand<wrap_operand_t<T>>::value...>::value, "at least one operand of in() is not valid");
-					return { *static_cast<const Base*>(this), wrap_operand_t<T>{t}... };
+					return { *static_cast<const Expr*>(this), wrap_operand_t<T>{t}... };
 				}
 		};
 
-	template<typename Base>
+	template<typename Expr>
 		struct alias_operators
 		{
 			template<typename alias_provider>
-				expression_alias_t<Base, alias_provider> as(const alias_provider&) const
+				expression_alias_t<Expr, alias_provider> as(const alias_provider&) const
 				{
-					return { *static_cast<const Base*>(this) };
+					return { *static_cast<const Expr*>(this) };
 				}
 		};
 
diff --git a/include/sqlpp11/boolean.h b/include/sqlpp11/boolean.h
index 848f2acf..c96ea101 100644
--- a/include/sqlpp11/boolean.h
+++ b/include/sqlpp11/boolean.h
@@ -44,28 +44,34 @@ namespace sqlpp
 		using _tag = ::sqlpp::tag::is_boolean;
 		using _cpp_value_type = bool;
 
-		struct _parameter_t
+		template<typename T>
+			using _is_valid_operand = is_boolean_t<T>;
+	};
+
+	template<>
+		struct parameter_value_t<boolean>
 		{
 			using _value_type = boolean; // FIXME
+			using _cpp_value_type = typename _value_type::_cpp_value_type;
 
-			_parameter_t():
+			parameter_value_t():
 				_value(false),
 				_is_null(true)
 			{}
 
-			_parameter_t(const _cpp_value_type& value):
+			parameter_value_t(const _cpp_value_type& value):
 				_value(value),
 				_is_null(false)
 			{}
 
-			_parameter_t& operator=(const _cpp_value_type& value)
+			parameter_value_t& operator=(const _cpp_value_type& value)
 			{
 				_value = value;
 				_is_null = false;
 				return *this;
 			}
 
-			_parameter_t& operator=(const tvin_t<wrap_operand_t<_cpp_value_type>>& t)
+			parameter_value_t& operator=(const tvin_t<wrap_operand_t<_cpp_value_type>>& t)
 			{
 				if (t._is_trivial())
 				{
@@ -80,7 +86,7 @@ namespace sqlpp
 				return *this;
 			}
 
-			_parameter_t& operator=(const std::nullptr_t&)
+			parameter_value_t& operator=(const std::nullptr_t&)
 			{
 				_value = false;
 				_is_null = true;
@@ -110,48 +116,41 @@ namespace sqlpp
 			bool _is_null;
 		};
 
+	template<typename Base>
+		struct expression_operators<Base, boolean>: public basic_expression_operators<Base, boolean>
+	{
 		template<typename T>
-			struct _is_valid_operand
+			using _is_valid_operand = is_valid_operand<boolean, T>;
+
+		template<typename T>
+			logical_and_t<Base, wrap_operand_t<T>> operator and(T t) const
 			{
-				static constexpr bool value = 
-					is_expression_t<T>::value // expressions are OK
-					and is_boolean_t<T>::value // the correct value type is required, of course
-					;
-			};
+				using rhs = wrap_operand_t<T>;
+				static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
 
-		template<typename Base>
-			struct expression_operators: public basic_expression_operators<Base, is_boolean_t>
-		{
-			template<typename T>
-				logical_and_t<Base, wrap_operand_t<T>> operator and(T t) const
-				{
-					using rhs = wrap_operand_t<T>;
-					static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
-
-					return { *static_cast<const Base*>(this), rhs{t} };
-				}
-
-			template<typename T>
-				logical_or_t<Base, wrap_operand_t<T>> operator or(T t) const
-				{
-					using rhs = wrap_operand_t<T>;
-					static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
-
-					return { *static_cast<const Base*>(this), rhs{t} };
-				}
-
-			logical_not_t<Base> operator not() const
-			{
-				return { *static_cast<const Base*>(this) };
+				return { *static_cast<const Base*>(this), rhs{t} };
 			}
-		};
 
-		template<typename Base>
-			struct column_operators
+		template<typename T>
+			logical_or_t<Base, wrap_operand_t<T>> operator or(T t) const
 			{
-			};
+				using rhs = wrap_operand_t<T>;
+				static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
+
+				return { *static_cast<const Base*>(this), rhs{t} };
+			}
+
+		logical_not_t<Base> operator not() const
+		{
+			return { *static_cast<const Base*>(this) };
+		}
 	};
 
+	template<typename Base>
+		struct column_operators<Base, boolean>
+		{
+		};
+
 	template<typename Db, typename FieldSpec>
 		struct result_field_t<boolean, Db, FieldSpec>: public result_field_methods_t<result_field_t<boolean, Db, FieldSpec>>
 	{
diff --git a/include/sqlpp11/boolean_expression.h b/include/sqlpp11/boolean_expression.h
index 5463f94f..5c8716f3 100644
--- a/include/sqlpp11/boolean_expression.h
+++ b/include/sqlpp11/boolean_expression.h
@@ -33,7 +33,7 @@
 namespace sqlpp
 {
 	template<typename Database>
-		struct boolean_expression_t: public boolean::template expression_operators<boolean_expression_t<Database>>
+		struct boolean_expression_t: public expression_operators<boolean_expression_t<Database>, boolean>
 		{
 			using _traits = make_traits<boolean, tag::is_expression>;
 			using _recursive_traits = make_recursive_traits<>;
diff --git a/include/sqlpp11/column.h b/include/sqlpp11/column.h
index 1ecbeb73..65700813 100644
--- a/include/sqlpp11/column.h
+++ b/include/sqlpp11/column.h
@@ -42,8 +42,9 @@
 namespace sqlpp
 {
 	template<typename Table, typename ColumnSpec>
-		struct column_t: public value_type_of<ColumnSpec>::template expression_operators<column_t<Table, ColumnSpec>>,
-		public value_type_of<ColumnSpec>::template column_operators<column_t<Table, ColumnSpec>>
+		struct column_t: 
+			public expression_operators<column_t<Table, ColumnSpec>, value_type_of<ColumnSpec>>,
+			public column_operators<column_t<Table, ColumnSpec>, value_type_of<ColumnSpec>>
 	{ 
 		struct _traits
 		{
@@ -66,7 +67,7 @@ namespace sqlpp
 		using _name_t = typename _spec_t::_name_t;
 
 		template<typename T>
-			using _is_valid_operand = typename value_type_of<ColumnSpec>::template _is_valid_operand<T>;
+			using _is_valid_operand = is_valid_operand<value_type_of<ColumnSpec>, T>;
 
 		column_t() = default;
 		column_t(const column_t&) = default;
diff --git a/include/sqlpp11/concat.h b/include/sqlpp11/concat.h
index 5e337f7b..19d3a819 100644
--- a/include/sqlpp11/concat.h
+++ b/include/sqlpp11/concat.h
@@ -36,8 +36,9 @@ namespace sqlpp
 {
 	// FIXME: Remove First, inherit from text_t
 	template<typename First, typename... Args>
-		struct concat_t: public value_type_of<First>::template expression_operators<concat_t<First, Args...>>,
-		public alias_operators<concat_t<First, Args...>>
+		struct concat_t: 
+			public expression_operators<concat_t<First, Args...>, value_type_of<First>>,
+			public alias_operators<concat_t<First, Args...>>
 	{
 		using _traits = make_traits<value_type_of<First>, ::sqlpp::tag::is_expression, ::sqlpp::tag::is_named_expression>;
 		using _recursive_traits = make_recursive_traits<First, Args...>;
diff --git a/include/sqlpp11/count.h b/include/sqlpp11/count.h
index 814dcf22..78aa258f 100644
--- a/include/sqlpp11/count.h
+++ b/include/sqlpp11/count.h
@@ -33,8 +33,9 @@
 namespace sqlpp
 {
 	template<typename Flag, typename Expr>
-		struct count_t: public sqlpp::integral::template expression_operators<count_t<Flag, Expr>>,
-		public alias_operators<count_t<Flag, Expr>>
+		struct count_t: 
+			public expression_operators<count_t<Flag, Expr>, integral>,
+			public alias_operators<count_t<Flag, Expr>>
 	{
 		using _traits = make_traits<::sqlpp::integral, ::sqlpp::tag::is_expression, ::sqlpp::tag::is_named_expression>;
 		using _recursive_traits = make_recursive_traits<Expr>;
diff --git a/include/sqlpp11/exists.h b/include/sqlpp11/exists.h
index 867933cf..7a1cc982 100644
--- a/include/sqlpp11/exists.h
+++ b/include/sqlpp11/exists.h
@@ -32,8 +32,9 @@
 namespace sqlpp
 {
 	template<typename Select>
-		struct exists_t: public boolean::template expression_operators<exists_t<Select>>,
-		public alias_operators<exists_t<Select>>
+		struct exists_t: 
+			public expression_operators<exists_t<Select>, boolean>,
+			public alias_operators<exists_t<Select>>
 	{
 		using _traits = make_traits<boolean, ::sqlpp::tag::is_expression, ::sqlpp::tag::is_named_expression>;
 		using _recursive_traits = make_recursive_traits<Select>;
diff --git a/include/sqlpp11/expression.h b/include/sqlpp11/expression.h
index 35982e16..2743502d 100644
--- a/include/sqlpp11/expression.h
+++ b/include/sqlpp11/expression.h
@@ -39,8 +39,9 @@
 namespace sqlpp
 {
 	template<typename Lhs, typename Rhs>
-		struct binary_expression_t<Lhs, op::equal_to, Rhs>: public ::sqlpp::boolean::template expression_operators<binary_expression_t<Lhs, op::equal_to, Rhs>>,
-		public alias_operators<binary_expression_t<Lhs, op::equal_to, Rhs>>
+		struct binary_expression_t<Lhs, op::equal_to, Rhs>:
+			public expression_operators<binary_expression_t<Lhs, op::equal_to, Rhs>, boolean>,
+			public alias_operators<binary_expression_t<Lhs, op::equal_to, Rhs>>
 		{
 			using _traits = make_traits<boolean, sqlpp::tag::is_expression>;
 			using _recursive_traits = make_recursive_traits<Lhs, Rhs>;
@@ -86,8 +87,9 @@ namespace sqlpp
 		};
 
 	template<typename Lhs, typename Rhs>
-		struct binary_expression_t<Lhs, op::not_equal_to, Rhs>: public ::sqlpp::boolean::template expression_operators<binary_expression_t<Lhs, op::not_equal_to, Rhs>>,
-		public alias_operators<binary_expression_t<Lhs, op::not_equal_to, Rhs>>
+		struct binary_expression_t<Lhs, op::not_equal_to, Rhs>:
+			public expression_operators<binary_expression_t<Lhs, op::not_equal_to, Rhs>, boolean>,
+			public alias_operators<binary_expression_t<Lhs, op::not_equal_to, Rhs>>
 		{
 			using _traits = make_traits<boolean, sqlpp::tag::is_expression>;
 			using _recursive_traits = make_recursive_traits<Lhs, Rhs>;
@@ -133,8 +135,9 @@ namespace sqlpp
 		};
 
 	template<typename Rhs>
-		struct unary_expression_t<op::logical_not, Rhs>: public ::sqlpp::boolean::template expression_operators<unary_expression_t<op::logical_not, Rhs>>,
-		public alias_operators<unary_expression_t<op::logical_not, Rhs>>
+		struct unary_expression_t<op::logical_not, Rhs>:
+			public expression_operators<unary_expression_t<op::logical_not, Rhs>, boolean>,
+			public alias_operators<unary_expression_t<op::logical_not, Rhs>>
 		{
 			using _traits = make_traits<boolean, sqlpp::tag::is_expression>;
 			using _recursive_traits = make_recursive_traits<Rhs>;
@@ -177,8 +180,9 @@ namespace sqlpp
 		};
 
 	template<typename Lhs, typename O, typename Rhs>
-		struct binary_expression_t: public value_type_of<O>::template expression_operators<binary_expression_t<Lhs, O, Rhs>>,
-		public alias_operators<binary_expression_t<Lhs, O, Rhs>>
+		struct binary_expression_t:
+			public expression_operators<binary_expression_t<Lhs, O, Rhs>, value_type_of<O>>,
+			public alias_operators<binary_expression_t<Lhs, O, Rhs>>
 	{
 		using _traits = make_traits<value_type_of<O>, sqlpp::tag::is_expression>;
 		using _recursive_traits = make_recursive_traits<Lhs, Rhs>;
@@ -215,8 +219,9 @@ namespace sqlpp
 		};
 
 	template<typename O, typename Rhs>
-		struct unary_expression_t: public value_type_of<O>::template expression_operators<unary_expression_t<O, Rhs>>,
-		public alias_operators<unary_expression_t<O, Rhs>>
+		struct unary_expression_t:
+			public expression_operators<unary_expression_t<O, Rhs>, value_type_of<O>>,
+			public alias_operators<unary_expression_t<O, Rhs>>
 	{
 		using _traits = make_traits<value_type_of<O>, sqlpp::tag::is_expression>;
 		using _recursive_traits = make_recursive_traits<Rhs>;
diff --git a/include/sqlpp11/floating_point.h b/include/sqlpp11/floating_point.h
index 400eceeb..60fd2bf3 100644
--- a/include/sqlpp11/floating_point.h
+++ b/include/sqlpp11/floating_point.h
@@ -42,28 +42,34 @@ namespace sqlpp
 		using _tag = ::sqlpp::tag::is_floating_point;
 		using _cpp_value_type = double;
 
-		struct _parameter_t
+		template<typename T>
+			using _is_valid_operand = is_numeric_t<T>;
+	};
+
+	template<>
+		struct parameter_value_t<floating_point>
 		{
 			using _value_type = floating_point;
+			using _cpp_value_type = typename _value_type::_cpp_value_type;
 
-			_parameter_t():
+			parameter_value_t():
 				_value(0),
 				_is_null(true)
 			{}
 
-			_parameter_t(const _cpp_value_type& value):
+			parameter_value_t(const _cpp_value_type& value):
 				_value(value),
 				_is_null(false)
 			{}
 
-			_parameter_t& operator=(const _cpp_value_type& value)
+			parameter_value_t& operator=(const _cpp_value_type& value)
 			{
 				_value = value;
 				_is_null = false;
 				return *this;
 			}
 
-			_parameter_t& operator=(const tvin_t<wrap_operand_t<_cpp_value_type>>& t)
+			parameter_value_t& operator=(const tvin_t<wrap_operand_t<_cpp_value_type>>& t)
 			{
 				if (t._is_trivial())
 				{
@@ -78,7 +84,7 @@ namespace sqlpp
 				return *this;
 			}
 
-			_parameter_t& operator=(const std::nullptr_t&)
+			parameter_value_t& operator=(const std::nullptr_t&)
 			{
 				_value = 0;
 				_is_null = true;
@@ -108,104 +114,112 @@ namespace sqlpp
 			bool _is_null;
 		};
 
-		template<typename T>
-			struct _is_valid_operand
-			{
-				static constexpr bool value = 
-					is_expression_t<T>::value // expressions are OK
-					and is_numeric_t<T>::value // the correct value type is required, of course
-					;
-			};
-
-		template<typename Base>
-			struct expression_operators: public basic_expression_operators<Base, is_numeric_t>
+	template<typename Expr>
+		struct expression_operators<Expr, floating_point>:
+			public basic_expression_operators<Expr, floating_point>
 		{
 			template<typename T>
-				plus_t<Base, floating_point, wrap_operand_t<T>> operator +(T t) const
+				struct _is_valid_operand
+				{
+					static constexpr bool value = 
+						is_expression_t<T>::value // expressions are OK
+						and floating_point::template _is_valid_operand<T>::value // the correct value type is required, of course
+						;
+				};
+
+			template<typename T>
+				plus_t<Expr, floating_point, wrap_operand_t<T>> operator +(T t) const
 				{
 					using rhs = wrap_operand_t<T>;
 					static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
 
-					return { *static_cast<const Base*>(this), rhs{t} };
+					return { *static_cast<const Expr*>(this), rhs{t} };
 				}
 
 			template<typename T>
-				minus_t<Base, floating_point, wrap_operand_t<T>> operator -(T t) const
+				minus_t<Expr, floating_point, wrap_operand_t<T>> operator -(T t) const
 				{
 					using rhs = wrap_operand_t<T>;
 					static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
 
-					return { *static_cast<const Base*>(this), rhs{t} };
+					return { *static_cast<const Expr*>(this), rhs{t} };
 				}
 
 			template<typename T>
-				multiplies_t<Base, floating_point, wrap_operand_t<T>> operator *(T t) const
+				multiplies_t<Expr, floating_point, wrap_operand_t<T>> operator *(T t) const
 				{
 					using rhs = wrap_operand_t<T>;
 
-					return { *static_cast<const Base*>(this), rhs{t} };
+					return { *static_cast<const Expr*>(this), rhs{t} };
 				}
 
 			template<typename T>
-				divides_t<Base, wrap_operand_t<T>> operator /(T t) const
+				divides_t<Expr, wrap_operand_t<T>> operator /(T t) const
 				{
 					using rhs = wrap_operand_t<T>;
 
-					return { *static_cast<const Base*>(this), rhs{t} };
+					return { *static_cast<const Expr*>(this), rhs{t} };
 				}
 
-			unary_plus_t<floating_point, Base> operator +() const
+			unary_plus_t<floating_point, Expr> operator +() const
 			{
-				return { *static_cast<const Base*>(this) };
+				return { *static_cast<const Expr*>(this) };
 			}
 
-			unary_minus_t<floating_point, Base> operator -() const
+			unary_minus_t<floating_point, Expr> operator -() const
 			{
-				return { *static_cast<const Base*>(this) };
+				return { *static_cast<const Expr*>(this) };
 			}
 		};
 
-		template<typename Base>
-			struct column_operators
-			{
-				template<typename T>
-					auto operator +=(T t) const -> assignment_t<Base, plus_t<Base, floating_point, wrap_operand_t<T>>>
-					{
-						using rhs = wrap_operand_t<T>;
-						static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
+	template<typename Column>
+		struct column_operators<Column, floating_point>
+		{
+			template<typename T>
+				struct _is_valid_operand
+				{
+					static constexpr bool value = 
+						is_expression_t<T>::value // expressions are OK
+						and floating_point::template _is_valid_operand<T>::value // the correct value type is required, of course
+						;
+				};
 
-						return { *static_cast<const Base*>(this), { *static_cast<const Base*>(this), rhs{t} } };
-					}
+			template<typename T>
+				auto operator +=(T t) const -> assignment_t<Column, plus_t<Column, floating_point, wrap_operand_t<T>>>
+				{
+					using rhs = wrap_operand_t<T>;
+					static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
 
-				template<typename T>
-					auto operator -=(T t) const -> assignment_t<Base, minus_t<Base, floating_point, wrap_operand_t<T>>>
-					{
-						using rhs = wrap_operand_t<T>;
-						static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
+					return { *static_cast<const Column*>(this), { *static_cast<const Column*>(this), rhs{t} } };
+				}
 
-						return { *static_cast<const Base*>(this), { *static_cast<const Base*>(this), rhs{t} } };
-					}
+			template<typename T>
+				auto operator -=(T t) const -> assignment_t<Column, minus_t<Column, floating_point, wrap_operand_t<T>>>
+				{
+					using rhs = wrap_operand_t<T>;
+					static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
 
-				template<typename T>
-					auto operator /=(T t) const -> assignment_t<Base, divides_t<Base, wrap_operand_t<T>>>
-					{
-						using rhs = wrap_operand_t<T>;
-						static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
+					return { *static_cast<const Column*>(this), { *static_cast<const Column*>(this), rhs{t} } };
+				}
 
-						return { *static_cast<const Base*>(this), { *static_cast<const Base*>(this), rhs{t} } };
-					}
+			template<typename T>
+				auto operator /=(T t) const -> assignment_t<Column, divides_t<Column, wrap_operand_t<T>>>
+				{
+					using rhs = wrap_operand_t<T>;
+					static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
 
-				template<typename T>
-					auto operator *=(T t) const -> assignment_t<Base, multiplies_t<Base, floating_point, wrap_operand_t<T>>>
-					{
-						using rhs = wrap_operand_t<T>;
-						static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
+					return { *static_cast<const Column*>(this), { *static_cast<const Column*>(this), rhs{t} } };
+				}
 
-						return { *static_cast<const Base*>(this), { *static_cast<const Base*>(this), rhs{t} } };
-					}
-			};
-	};
+			template<typename T>
+				auto operator *=(T t) const -> assignment_t<Column, multiplies_t<Column, floating_point, wrap_operand_t<T>>>
+				{
+					using rhs = wrap_operand_t<T>;
+					static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
 
+					return { *static_cast<const Column*>(this), { *static_cast<const Column*>(this), rhs{t} } };
+				}
+		};
 	template<typename Db, typename FieldSpec>
 		struct result_field_t<floating_point, Db, FieldSpec>: public result_field_methods_t<result_field_t<floating_point, Db, FieldSpec>>
 		{
diff --git a/include/sqlpp11/in.h b/include/sqlpp11/in.h
index f014d137..59b5d792 100644
--- a/include/sqlpp11/in.h
+++ b/include/sqlpp11/in.h
@@ -35,8 +35,9 @@
 namespace sqlpp
 {
 	template<bool NotInverted, typename Operand, typename... Args>
-		struct in_t: public boolean::template expression_operators<in_t<NotInverted, Operand, Args...>>,
-		public alias_operators<in_t<NotInverted, Operand, Args...>>
+		struct in_t:
+			public expression_operators<in_t<NotInverted, Operand, Args...>, boolean>,
+			public alias_operators<in_t<NotInverted, Operand, Args...>>
 	{
 		using _traits = make_traits<boolean, ::sqlpp::tag::is_expression, ::sqlpp::tag::is_named_expression>;
 		using _recursive_traits = make_recursive_traits<Operand, Args...>;
diff --git a/include/sqlpp11/integral.h b/include/sqlpp11/integral.h
index feef4446..eb5915f9 100644
--- a/include/sqlpp11/integral.h
+++ b/include/sqlpp11/integral.h
@@ -44,199 +44,212 @@ namespace sqlpp
 		using _tag = ::sqlpp::tag::is_integral;
 		using _cpp_value_type = int64_t;
 
-		struct _parameter_t
+		template<typename T>
+			using _is_valid_operand = is_numeric_t<T>;
+	};
+
+	template<>
+	struct parameter_value_t<integral>
+	{
+		using _value_type = integral;
+		using _cpp_value_type = typename _value_type::_cpp_value_type;
+
+		parameter_value_t():
+			_value(0),
+			_is_null(true)
+		{}
+
+		explicit parameter_value_t(const _cpp_value_type& value):
+			_value(value),
+			_is_null(false)
+		{}
+
+		parameter_value_t& operator=(const _cpp_value_type& value)
 		{
-			using _value_type = integral;
+			_value = value;
+			_is_null = false;
+			return *this;
+		}
 
-			_parameter_t():
-				_value(0),
-				_is_null(true)
-			{}
-
-			explicit _parameter_t(const _cpp_value_type& value):
-				_value(value),
-				_is_null(false)
-			{}
-
-			_parameter_t& operator=(const _cpp_value_type& value)
-			{
-				_value = value;
-				_is_null = false;
-				return *this;
-			}
-
-			_parameter_t& operator=(const tvin_t<wrap_operand_t<_cpp_value_type>>& t)
-			{
-				if (t._is_trivial())
-				{
-					_value = 0;
-					_is_null = true;
-				}
-				else
-				{
-					_value = t._value._t;
-					_is_null = false;
-				}
-				return *this;
-			}
-
-			void set_null()
+		parameter_value_t& operator=(const tvin_t<wrap_operand_t<_cpp_value_type>>& t)
+		{
+			if (t._is_trivial())
 			{
 				_value = 0;
 				_is_null = true;
 			}
-
-			bool is_null() const
-			{ 
-				return _is_null; 
-			}
-
-			const _cpp_value_type& value() const
+			else
 			{
-				return _value;
+				_value = t._value._t;
+				_is_null = false;
+			}
+			return *this;
+		}
+
+		void set_null()
+		{
+			_value = 0;
+			_is_null = true;
+		}
+
+		bool is_null() const
+		{ 
+			return _is_null; 
+		}
+
+		const _cpp_value_type& value() const
+		{
+			return _value;
+		}
+
+		operator _cpp_value_type() const { return _value; }
+
+		template<typename Target>
+			void _bind(Target& target, size_t index) const
+			{
+				target._bind_integral_parameter(index, &_value, _is_null);
 			}
 
-			operator _cpp_value_type() const { return _value; }
-
-			template<typename Target>
-				void _bind(Target& target, size_t index) const
-				{
-					target._bind_integral_parameter(index, &_value, _is_null);
-				}
-
-		private:
-			_cpp_value_type _value;
-			bool _is_null;
-		};
+	private:
+		_cpp_value_type _value;
+		bool _is_null;
+	};
 
+	template<typename Base>
+		struct expression_operators<Base, integral>: public basic_expression_operators<Base, integral>
+	{
 		template<typename T>
 			struct _is_valid_operand
 			{
 				static constexpr bool value = 
 					is_expression_t<T>::value // expressions are OK
-					and is_numeric_t<T>::value // the correct value type is required, of course
+					and integral::template _is_valid_operand<T>::value // the correct value type is required, of course
 					;
 			};
 
-		template<typename Base>
-			struct expression_operators: public basic_expression_operators<Base, is_numeric_t>
+		template<typename T>
+			plus_t<Base, value_type_t<T>, wrap_operand_t<T>> operator +(T t) const
+			{
+				using rhs = wrap_operand_t<T>;
+				static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
+
+				return { *static_cast<const Base*>(this), {t} };
+			}
+
+		template<typename T>
+			minus_t<Base, value_type_t<T>, wrap_operand_t<T>> operator -(T t) const
+			{
+				using rhs = wrap_operand_t<T>;
+				static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
+
+				return { *static_cast<const Base*>(this), {t} };
+			}
+
+		template<typename T>
+			multiplies_t<Base, value_type_t<T>, wrap_operand_t<T>> operator *(T t) const
+			{
+				using rhs = wrap_operand_t<T>;
+				static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
+
+				return { *static_cast<const Base*>(this), {t} };
+			}
+
+		template<typename T>
+			divides_t<Base, wrap_operand_t<T>> operator /(T t) const
+			{
+				using rhs = wrap_operand_t<T>;
+				static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
+
+				return { *static_cast<const Base*>(this), {t} };
+			}
+
+		template<typename T>
+			modulus_t<Base, wrap_operand_t<T>> operator %(T t) const
+			{
+				using rhs = wrap_operand_t<T>;
+				static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
+
+				return { *static_cast<const Base*>(this), {t} };
+			}
+
+		unary_plus_t<integral, Base> operator +() const
 		{
-			template<typename T>
-				plus_t<Base, value_type_t<T>, wrap_operand_t<T>> operator +(T t) const
-				{
-					using rhs = wrap_operand_t<T>;
-					static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
+			return { *static_cast<const Base*>(this) };
+		}
 
-					return { *static_cast<const Base*>(this), {t} };
-				}
+		unary_minus_t<integral, Base> operator -() const
+		{
+			return { *static_cast<const Base*>(this) };
+		}
 
-			template<typename T>
-				minus_t<Base, value_type_t<T>, wrap_operand_t<T>> operator -(T t) const
-				{
-					using rhs = wrap_operand_t<T>;
-					static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
-
-					return { *static_cast<const Base*>(this), {t} };
-				}
-
-			template<typename T>
-				multiplies_t<Base, value_type_t<T>, wrap_operand_t<T>> operator *(T t) const
-				{
-					using rhs = wrap_operand_t<T>;
-					static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
-
-					return { *static_cast<const Base*>(this), {t} };
-				}
-
-			template<typename T>
-				divides_t<Base, wrap_operand_t<T>> operator /(T t) const
-				{
-					using rhs = wrap_operand_t<T>;
-					static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
-
-					return { *static_cast<const Base*>(this), {t} };
-				}
-
-			template<typename T>
-				modulus_t<Base, wrap_operand_t<T>> operator %(T t) const
-				{
-					using rhs = wrap_operand_t<T>;
-					static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
-
-					return { *static_cast<const Base*>(this), {t} };
-				}
-
-			unary_plus_t<integral, Base> operator +() const
+		template<typename T>
+			bitwise_and_t<Base, value_type_t<T>, wrap_operand_t<T>> operator &(T t) const
 			{
-				return { *static_cast<const Base*>(this) };
+				using rhs = wrap_operand_t<T>;
+				static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
+
+				return { *static_cast<const Base*>(this), {t} };
 			}
 
-			unary_minus_t<integral, Base> operator -() const
+		template<typename T>
+			bitwise_or_t<Base, value_type_t<T>, wrap_operand_t<T>> operator |(T t) const
 			{
-				return { *static_cast<const Base*>(this) };
+				using rhs = wrap_operand_t<T>;
+				static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
+
+				return { *static_cast<const Base*>(this), {t} };
 			}
 
-			template<typename T>
-				bitwise_and_t<Base, value_type_t<T>, wrap_operand_t<T>> operator &(T t) const
-				{
-					using rhs = wrap_operand_t<T>;
-					static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
-
-					return { *static_cast<const Base*>(this), {t} };
-				}
-
-			template<typename T>
-				bitwise_or_t<Base, value_type_t<T>, wrap_operand_t<T>> operator |(T t) const
-				{
-					using rhs = wrap_operand_t<T>;
-					static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
-
-					return { *static_cast<const Base*>(this), {t} };
-				}
-
-		};
-
-		template<typename Base>
-			struct column_operators
-			{
-				template<typename T>
-					auto operator +=(T t) const -> assignment_t<Base, plus_t<Base, value_type_t<T>, wrap_operand_t<T>>>
-					{
-						using rhs = wrap_operand_t<T>;
-						static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
-
-						return { *static_cast<const Base*>(this), {{*static_cast<const Base*>(this), rhs{t}}}};
-					}
-
-				template<typename T>
-					auto operator -=(T t) const -> assignment_t<Base, minus_t<Base, value_type_t<T>, wrap_operand_t<T>>>
-					{
-						using rhs = wrap_operand_t<T>;
-						static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
-
-						return { *static_cast<const Base*>(this), {{*static_cast<const Base*>(this), rhs{t}}}};
-					}
-
-				template<typename T>
-					auto operator /=(T t) const -> assignment_t<Base, divides_t<Base, wrap_operand_t<T>>>
-					{
-						using rhs = wrap_operand_t<T>;
-						static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
-
-						return { *static_cast<const Base*>(this), {{*static_cast<const Base*>(this), rhs{t}}}};
-					}
-
-				template<typename T>
-					auto operator *=(T t) const -> assignment_t<Base, multiplies_t<Base, value_type_t<T>, wrap_operand_t<T>>>
-					{
-						using rhs = wrap_operand_t<T>;
-						static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
-
-						return { *static_cast<const Base*>(this), {{*static_cast<const Base*>(this), rhs{t}}}};
-					}
-			};
 	};
 
+	template<typename Base>
+		struct column_operators<Base, integral>
+		{
+			template<typename T>
+				struct _is_valid_operand
+				{
+					static constexpr bool value = 
+						is_expression_t<T>::value // expressions are OK
+						and integral::template _is_valid_operand<T>::value // the correct value type is required, of course
+						;
+				};
+
+			template<typename T>
+				auto operator +=(T t) const -> assignment_t<Base, plus_t<Base, value_type_t<T>, wrap_operand_t<T>>>
+				{
+					using rhs = wrap_operand_t<T>;
+					static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
+
+					return { *static_cast<const Base*>(this), {{*static_cast<const Base*>(this), rhs{t}}}};
+				}
+
+			template<typename T>
+				auto operator -=(T t) const -> assignment_t<Base, minus_t<Base, value_type_t<T>, wrap_operand_t<T>>>
+				{
+					using rhs = wrap_operand_t<T>;
+					static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
+
+					return { *static_cast<const Base*>(this), {{*static_cast<const Base*>(this), rhs{t}}}};
+				}
+
+			template<typename T>
+				auto operator /=(T t) const -> assignment_t<Base, divides_t<Base, wrap_operand_t<T>>>
+				{
+					using rhs = wrap_operand_t<T>;
+					static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
+
+					return { *static_cast<const Base*>(this), {{*static_cast<const Base*>(this), rhs{t}}}};
+				}
+
+			template<typename T>
+				auto operator *=(T t) const -> assignment_t<Base, multiplies_t<Base, value_type_t<T>, wrap_operand_t<T>>>
+				{
+					using rhs = wrap_operand_t<T>;
+					static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
+
+					return { *static_cast<const Base*>(this), {{*static_cast<const Base*>(this), rhs{t}}}};
+				}
+		};
 
 	template<typename Db, typename FieldSpec>
 		struct result_field_t<integral, Db, FieldSpec>: public result_field_methods_t<result_field_t<integral, Db, FieldSpec>>
diff --git a/include/sqlpp11/is_null.h b/include/sqlpp11/is_null.h
index 3fef25ab..fbc2ef03 100644
--- a/include/sqlpp11/is_null.h
+++ b/include/sqlpp11/is_null.h
@@ -34,8 +34,9 @@
 namespace sqlpp
 {
 	template<bool NotInverted, typename Operand>
-		struct is_null_t: public boolean::template expression_operators<is_null_t<NotInverted, Operand>>,
-		public alias_operators<is_null_t<NotInverted, Operand>>
+		struct is_null_t:
+			public expression_operators<is_null_t<NotInverted, Operand>, boolean>,
+			public alias_operators<is_null_t<NotInverted, Operand>>
 	{
 		using _traits = make_traits<boolean, ::sqlpp::tag::is_expression, ::sqlpp::tag::is_named_expression>;
 		using _recursive_traits = make_recursive_traits<Operand>;
diff --git a/include/sqlpp11/like.h b/include/sqlpp11/like.h
index bbb7763e..d6bede32 100644
--- a/include/sqlpp11/like.h
+++ b/include/sqlpp11/like.h
@@ -34,8 +34,9 @@
 namespace sqlpp
 {
 	template<typename Operand, typename Pattern>
-		struct like_t: public boolean::template expression_operators<like_t<Operand, Pattern>>,
-		public alias_operators<like_t<Operand, Pattern>>
+		struct like_t:
+			public expression_operators<like_t<Operand, Pattern>, boolean>,
+			public alias_operators<like_t<Operand, Pattern>>
 	{
 		using _traits = make_traits<boolean, ::sqlpp::tag::is_expression, ::sqlpp::tag::is_named_expression>;
 		using _recursive_traits = make_recursive_traits<Operand, Pattern>;
diff --git a/include/sqlpp11/max.h b/include/sqlpp11/max.h
index b6e006d4..8edce697 100644
--- a/include/sqlpp11/max.h
+++ b/include/sqlpp11/max.h
@@ -32,8 +32,9 @@
 namespace sqlpp
 {
 	template<typename Expr>
-		struct max_t: public value_type_of<Expr>::template expression_operators<max_t<Expr>>,
-		public alias_operators<max_t<Expr>>
+		struct max_t:
+			public expression_operators<max_t<Expr>, value_type_of<Expr>>,
+			public alias_operators<max_t<Expr>>
 	{
 		using _traits = make_traits<value_type_of<Expr>, ::sqlpp::tag::is_expression, ::sqlpp::tag::is_named_expression>;
 		using _recursive_traits = make_recursive_traits<Expr>;
diff --git a/include/sqlpp11/min.h b/include/sqlpp11/min.h
index d7788213..1aac755f 100644
--- a/include/sqlpp11/min.h
+++ b/include/sqlpp11/min.h
@@ -32,8 +32,9 @@
 namespace sqlpp
 {
 	template<typename Expr>
-		struct min_t: public value_type_of<Expr>::template expression_operators<min_t<Expr>>,
-		public alias_operators<min_t<Expr>>
+		struct min_t:
+			public expression_operators<min_t<Expr>, value_type_of<Expr>>,
+			public alias_operators<min_t<Expr>>
 	{
 		using _traits = make_traits<value_type_of<Expr>, ::sqlpp::tag::is_expression, ::sqlpp::tag::is_named_expression>;
 		using _recursive_traits = make_recursive_traits<Expr>;
diff --git a/include/sqlpp11/no_value.h b/include/sqlpp11/no_value.h
index c5ec11fa..be1877d1 100644
--- a/include/sqlpp11/no_value.h
+++ b/include/sqlpp11/no_value.h
@@ -28,28 +28,24 @@
 #define SQLPP_NO_VALUE_H
 
 #include <type_traits>
+#include <sqlpp11/value_type_fwd.h>
 
 namespace sqlpp
 {
 	struct no_value_t
 	{
 		using _tag = void;
-		template<typename T>
-			struct _is_valid_operand
-			{
-				static constexpr bool value = false;
-			};
-
-		template<typename Base>
-			struct expression_operators
-			{
-			};
-
-		template<typename Base>
-			struct column_operators
-			{
-			};
 	};
 
+	template<typename Base>
+		struct expression_operators<Base, no_value_t>
+		{
+		};
+
+	template<typename Base>
+		struct column_operators<Base, no_value_t>
+		{
+		};
+
 }
 #endif
diff --git a/include/sqlpp11/parameter.h b/include/sqlpp11/parameter.h
index 665523f9..a789f56f 100644
--- a/include/sqlpp11/parameter.h
+++ b/include/sqlpp11/parameter.h
@@ -34,7 +34,8 @@
 namespace sqlpp
 {
 	template<typename ValueType, typename NameType>
-		struct parameter_t: public ValueType::template expression_operators<parameter_t<ValueType, NameType>>
+		struct parameter_t:
+			public expression_operators<parameter_t<ValueType, NameType>, ValueType>
 	{
 		using _traits = make_traits<ValueType, tag::is_parameter, tag::is_expression>;
 		struct _recursive_traits
@@ -47,7 +48,7 @@ namespace sqlpp
 			using _can_be_null = std::true_type;
 		};
 
-		using _instance_t = typename NameType::_name_t::template _member_t<typename ValueType::_parameter_t>;
+		using _instance_t = member_t<NameType, parameter_value_t<ValueType>>;
 
 		parameter_t()
 		{}
diff --git a/include/sqlpp11/statement.h b/include/sqlpp11/statement.h
index 615a50cb..d427374a 100644
--- a/include/sqlpp11/statement.h
+++ b/include/sqlpp11/statement.h
@@ -122,7 +122,7 @@ namespace sqlpp
 			>
 			struct statement_t:
 				public Policies::template _member_t<detail::statement_policies_t<Db, Policies...>>...,
-				public detail::statement_policies_t<Db, Policies...>::_value_type::template expression_operators<statement_t<Db, Policies...>>,
+				public expression_operators<statement_t<Db, Policies...>, value_type_of<detail::statement_policies_t<Db, Policies...>>>,
 				public detail::statement_policies_t<Db, Policies...>::_result_methods_t,
 				public Policies::template _methods_t<detail::statement_policies_t<Db, Policies...>>...
 	{
diff --git a/include/sqlpp11/sum.h b/include/sqlpp11/sum.h
index 8e3553f3..2cb26d0b 100644
--- a/include/sqlpp11/sum.h
+++ b/include/sqlpp11/sum.h
@@ -32,8 +32,9 @@
 namespace sqlpp
 {
 	template<typename Flag, typename Expr>
-		struct sum_t: public value_type_of<Expr>::template expression_operators<sum_t<Flag, Expr>>,
-		public alias_operators<sum_t<Flag, Expr>>
+		struct sum_t:
+			public expression_operators<sum_t<Flag, Expr>, value_type_of<Expr>>,
+			public alias_operators<sum_t<Flag, Expr>>
 	{
 		using _traits = make_traits<value_type_of<Expr>, ::sqlpp::tag::is_expression, ::sqlpp::tag::is_named_expression>;
 		using _recursive_traits = make_recursive_traits<Expr>;
diff --git a/include/sqlpp11/table.h b/include/sqlpp11/table.h
index 06a1c2f5..8a072037 100644
--- a/include/sqlpp11/table.h
+++ b/include/sqlpp11/table.h
@@ -40,7 +40,10 @@ namespace sqlpp
 	struct table_base_t {};
 
 	template<typename Table, typename... ColumnSpec>
-		struct table_t: public table_base_t, public ColumnSpec::_name_t::template _member_t<column_t<Table, ColumnSpec>>...
+		struct table_t: 
+			public table_base_t, 
+			//public ColumnSpec::_name_t::template _member_t<column_t<Table, ColumnSpec>>...
+			public member_t<ColumnSpec, column_t<Table, ColumnSpec>>...
 	{
 		using _traits = make_traits<no_value_t, tag::is_table>;
 
diff --git a/include/sqlpp11/text.h b/include/sqlpp11/text.h
index 258603aa..5ecd5841 100644
--- a/include/sqlpp11/text.h
+++ b/include/sqlpp11/text.h
@@ -43,28 +43,34 @@ namespace sqlpp
 		using _tag = ::sqlpp::tag::is_text;
 		using _cpp_value_type = std::string;
 
-		struct _parameter_t
+		template<typename T>
+			using _is_valid_operand = is_text_t<T>;
+	};
+
+	template<>
+		struct parameter_value_t<text>
 		{
 			using _value_type = text;
+			using _cpp_value_type = typename _value_type::_cpp_value_type;
 
-			_parameter_t():
+			parameter_value_t():
 				_value(""),
 				_is_null(true)
 			{}
 
-			_parameter_t(const _cpp_value_type& value):
+			parameter_value_t(const _cpp_value_type& value):
 				_value(value),
 				_is_null(false)
 			{}
 
-			_parameter_t& operator=(const _cpp_value_type& value)
+			parameter_value_t& operator=(const _cpp_value_type& value)
 			{
 				_value = value;
 				_is_null = false;
 				return *this;
 			}
 
-			_parameter_t& operator=(const tvin_t<wrap_operand_t<_cpp_value_type>>& t)
+			parameter_value_t& operator=(const tvin_t<wrap_operand_t<_cpp_value_type>>& t)
 			{
 				if (t._is_trivial())
 				{
@@ -79,7 +85,7 @@ namespace sqlpp
 				return *this;
 			}
 
-			_parameter_t& operator=(const std::nullptr_t&)
+			parameter_value_t& operator=(const std::nullptr_t&)
 			{
 				_value = "";
 				_is_null = true;
@@ -110,51 +116,47 @@ namespace sqlpp
 		};
 
 
+	template<typename Base>
+		struct expression_operators<Base, text>: public basic_expression_operators<Base, text>
+	{
 		template<typename T>
-			struct _is_valid_operand
-			{
-				static constexpr bool value = 
-					is_expression_t<T>::value // expressions are OK
-					and is_text_t<T>::value // the correct value type is required, of course
-					;
-			};
+			using _is_valid_operand = is_valid_operand<text, T>;
 
-		template<typename Base>
-			struct expression_operators: public basic_expression_operators<Base, is_text_t>
+		template<typename T>
+			concat_t<Base, wrap_operand_t<T>> operator+(T t) const
+			{
+				using rhs = wrap_operand_t<T>;
+				static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
+
+				return { *static_cast<const Base*>(this), {t} };
+			}
+
+		template<typename T>
+			like_t<Base, wrap_operand_t<T>> like(T t) const
+			{
+				using rhs = wrap_operand_t<T>;
+				static_assert(_is_valid_operand<rhs>::value, "invalid argument for like()");
+
+				return { *static_cast<const Base*>(this), {t} };
+			}
+	};
+
+	template<typename Base>
+		struct column_operators<Base, text>
 		{
 			template<typename T>
-				concat_t<Base, wrap_operand_t<T>> operator+(T t) const
-				{
-					using rhs = wrap_operand_t<T>;
-					static_assert(_is_valid_operand<rhs>::value, "invalid rhs operand");
-
-					return { *static_cast<const Base*>(this), {t} };
-				}
+				using _is_valid_operand = is_valid_operand<text, T>;
 
 			template<typename T>
-				like_t<Base, wrap_operand_t<T>> like(T t) const
+				auto operator +=(T t) const -> assignment_t<Base, concat_t<Base, wrap_operand_t<T>>>
 				{
 					using rhs = wrap_operand_t<T>;
-					static_assert(_is_valid_operand<rhs>::value, "invalid argument for like()");
+					static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
 
-					return { *static_cast<const Base*>(this), {t} };
+					return { *static_cast<const Base*>(this), concat_t<Base, wrap_operand_t<T>>{ *static_cast<const Base*>(this), rhs{t} } };
 				}
 		};
 
-		template<typename Base>
-			struct column_operators
-			{
-				template<typename T>
-					auto operator +=(T t) const -> assignment_t<Base, concat_t<Base, wrap_operand_t<T>>>
-					{
-						using rhs = wrap_operand_t<T>;
-						static_assert(_is_valid_operand<rhs>::value, "invalid rhs assignment operand");
-
-						return { *static_cast<const Base*>(this), concat_t<Base, wrap_operand_t<T>>{ *static_cast<const Base*>(this), rhs{t} } };
-					}
-			};
-	};
-
 	template<typename Db, typename FieldSpec>
 		struct result_field_t<text, Db, FieldSpec>: public result_field_methods_t<result_field_t<text, Db, FieldSpec>>
 	{
diff --git a/include/sqlpp11/type_traits.h b/include/sqlpp11/type_traits.h
index 9b30d438..1a7403e8 100644
--- a/include/sqlpp11/type_traits.h
+++ b/include/sqlpp11/type_traits.h
@@ -232,6 +232,9 @@ namespace sqlpp
 			using _can_be_null = detail::any_t<can_be_null_t<Arguments>::value...>;
 		};
 
+	template<typename NameProvider, typename Member>
+		using member_t = typename NameProvider::_name_t::template _member_t<Member>;
+
 }
 
 #endif
diff --git a/include/sqlpp11/value_type_fwd.h b/include/sqlpp11/value_type_fwd.h
new file mode 100644
index 00000000..805e5662
--- /dev/null
+++ b/include/sqlpp11/value_type_fwd.h
@@ -0,0 +1,65 @@
+/*
+ * 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_VALUE_TYPE_FWD_H
+#define SQLPP_VALUE_TYPE_FWD_H
+
+#include <sqlpp11/wrong.h>
+#include <sqlpp11/type_traits.h>
+
+namespace sqlpp
+{
+	template<typename ValueType>
+		struct parameter_value_t
+		{
+			static_assert(wrong_t<parameter_value_t>::value, "Missing parameter value type for ValueType");
+		};
+
+	template<typename Column, typename ValueType>
+		struct column_operators
+		{
+			static_assert(wrong_t<column_operators>::value, "Missing column operators for ValueType");
+		};
+
+	template<typename Expr, typename ValueType>
+		struct expression_operators
+		{
+			static_assert(wrong_t<expression_operators>::value, "Missing expression operators for ValueType");
+		};
+
+	template<typename ValueType, typename T>
+		struct is_valid_operand
+		{
+			static constexpr bool value = 
+				is_expression_t<T>::value // expressions are OK
+				and ValueType::template _is_valid_operand<T>::value // the correct value type is required, of course
+				;
+		};
+}
+
+#endif
+
+
diff --git a/include/sqlpp11/verbatim.h b/include/sqlpp11/verbatim.h
index a148519b..21322564 100644
--- a/include/sqlpp11/verbatim.h
+++ b/include/sqlpp11/verbatim.h
@@ -33,8 +33,9 @@
 namespace sqlpp
 {
 	template<typename ValueType> // Csaba Csoma suggests: unsafe_sql instead of verbatim
-		struct verbatim_t: public ValueType::template expression_operators<verbatim_t<ValueType>>,
-		public alias_operators<verbatim_t<ValueType>>
+		struct verbatim_t:
+			public expression_operators<verbatim_t<ValueType>, ValueType>,
+			public alias_operators<verbatim_t<ValueType>>
 	{
 		using _traits = make_traits<ValueType, ::sqlpp::tag::is_expression>;
 		struct _recursive_traits : public make_recursive_traits<>
diff --git a/tests/PreparedTest.cpp b/tests/PreparedTest.cpp
index cacac316..27a5832e 100644
--- a/tests/PreparedTest.cpp
+++ b/tests/PreparedTest.cpp
@@ -81,9 +81,9 @@ int main()
 		using Exp = decltype((t.beta.like(parameter(t.beta)) and t.alpha == parameter(t.alpha)) or t.gamma != parameter(t.gamma));
 		using T = sqlpp::make_parameter_list_t<Exp>;
 		T npl;
-		static_assert(std::is_same<typename sqlpp::value_type_of<decltype(t.alpha)>::_parameter_t, decltype(npl.alpha)>::value, "type requirement");
-		static_assert(std::is_same<typename sqlpp::value_type_of<decltype(t.beta)>::_parameter_t, decltype(npl.beta)>::value, "type requirement");
-		static_assert(std::is_same<typename sqlpp::value_type_of<decltype(t.gamma)>::_parameter_t, decltype(npl.gamma)>::value, "type requirement");
+		static_assert(std::is_same<sqlpp::parameter_value_t<sqlpp::value_type_of<decltype(t.alpha)>>, decltype(npl.alpha)>::value, "type requirement");
+		static_assert(std::is_same<sqlpp::parameter_value_t<sqlpp::value_type_of<decltype(t.beta)>>, decltype(npl.beta)>::value, "type requirement");
+		static_assert(std::is_same<sqlpp::parameter_value_t<sqlpp::value_type_of<decltype(t.gamma)>>, decltype(npl.gamma)>::value, "type requirement");
 	}
 
 	// Wonderful, now take a look at the parameter list of a select
@@ -96,9 +96,9 @@ int main()
 		using T = sqlpp::make_parameter_list_t<S>;
 		T npl;
 
-		static_assert(std::is_same<typename sqlpp::value_type_of<decltype(t.alpha)>::_parameter_t, decltype(npl.alpha)>::value, "type requirement");
-		static_assert(std::is_same<typename sqlpp::value_type_of<decltype(t.beta)>::_parameter_t, decltype(npl.beta)>::value, "type requirement");
-		static_assert(std::is_same<typename sqlpp::value_type_of<decltype(t.gamma)>::_parameter_t, decltype(npl.gamma)>::value, "type requirement");
+		static_assert(std::is_same<sqlpp::parameter_value_t<sqlpp::value_type_of<decltype(t.alpha)>>, decltype(npl.alpha)>::value, "type requirement");
+		static_assert(std::is_same<sqlpp::parameter_value_t<sqlpp::value_type_of<decltype(t.beta)>>, decltype(npl.beta)>::value, "type requirement");
+		static_assert(std::is_same<sqlpp::parameter_value_t<sqlpp::value_type_of<decltype(t.gamma)>>, decltype(npl.gamma)>::value, "type requirement");
 		npl.alpha = 7;
 		auto x = npl;
 		x = npl;