From 55324d1f71646fd1c54f4d2629a46b58d87979c7 Mon Sep 17 00:00:00 2001
From: Roland Bock <rbock@eudoxos.de>
Date: Sat, 17 Aug 2024 21:11:52 +0200
Subject: [PATCH] New tuple_to_sql_string

---
 include/sqlpp11/core/clause/cte.h             |  2 +-
 include/sqlpp11/core/clause/from.h            |  2 +-
 include/sqlpp11/core/clause/group_by.h        |  4 +-
 include/sqlpp11/core/clause/having.h          |  2 +-
 .../sqlpp11/core/clause/insert_value_list.h   | 10 +--
 include/sqlpp11/core/clause/order_by.h        |  4 +-
 .../sqlpp11/core/clause/select_column_list.h  |  4 +-
 .../sqlpp11/core/clause/select_flag_list.h    |  4 +-
 include/sqlpp11/core/clause/select_flags.h    |  2 +-
 include/sqlpp11/core/clause/union.h           |  2 +-
 include/sqlpp11/core/clause/union_flags.h     |  2 +-
 include/sqlpp11/core/clause/update_list.h     |  4 +-
 include/sqlpp11/core/clause/using.h           |  6 +-
 include/sqlpp11/core/clause/where.h           |  2 +-
 include/sqlpp11/core/clause/with.h            |  4 +-
 .../sqlpp11/core/database/parameter_list.h    |  2 +-
 include/sqlpp11/core/operator/in_expression.h |  5 +-
 include/sqlpp11/core/query/custom_query.h     |  4 +-
 ...nterpret_tuple.h => tuple_to_sql_string.h} | 87 ++++++++++++-------
 include/sqlpp11/mysql/serializer.h            | 12 +--
 .../postgresql/on_conflict_do_update.h        | 12 +--
 .../postgresql/returning_column_list.h        |  9 +-
 22 files changed, 99 insertions(+), 86 deletions(-)
 rename include/sqlpp11/core/{interpret_tuple.h => tuple_to_sql_string.h} (52%)

diff --git a/include/sqlpp11/core/clause/cte.h b/include/sqlpp11/core/clause/cte.h
index 88a7c09e..ab6fecef 100644
--- a/include/sqlpp11/core/clause/cte.h
+++ b/include/sqlpp11/core/clause/cte.h
@@ -26,7 +26,7 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/logic.h>
 #include <sqlpp11/core/query/result_row.h>
 #include <sqlpp11/core/clause/select_flags.h>
diff --git a/include/sqlpp11/core/clause/from.h b/include/sqlpp11/core/clause/from.h
index 5bdf2490..d4732362 100644
--- a/include/sqlpp11/core/clause/from.h
+++ b/include/sqlpp11/core/clause/from.h
@@ -26,7 +26,7 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/logic.h>
 #include <sqlpp11/core/no_data.h>
 #include <sqlpp11/core/query/policy_update.h>
diff --git a/include/sqlpp11/core/clause/group_by.h b/include/sqlpp11/core/clause/group_by.h
index 687a3798..691b2b26 100644
--- a/include/sqlpp11/core/clause/group_by.h
+++ b/include/sqlpp11/core/clause/group_by.h
@@ -26,7 +26,7 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/logic.h>
 #include <sqlpp11/core/query/policy_update.h>
 #include <sqlpp11/core/type_traits.h>
@@ -153,7 +153,7 @@ namespace sqlpp
   template <typename Context, typename... Columns>
   auto to_sql_string(Context& context, const group_by_data_t<Columns...>& t) -> std::string
   {
-    return " GROUP BY " + interpret_tuple(t._columns, ',', context);
+    return " GROUP BY " + tuple_to_sql_string(context, t._columns, tuple_operand{", "});
   }
 
   template <typename... T>
diff --git a/include/sqlpp11/core/clause/having.h b/include/sqlpp11/core/clause/having.h
index f455a292..214799c4 100644
--- a/include/sqlpp11/core/clause/having.h
+++ b/include/sqlpp11/core/clause/having.h
@@ -26,7 +26,7 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/logic.h>
 #include <sqlpp11/core/query/policy_update.h>
 #include <sqlpp11/core/type_traits.h>
diff --git a/include/sqlpp11/core/clause/insert_value_list.h b/include/sqlpp11/core/clause/insert_value_list.h
index ff2e4ed0..90831ec2 100644
--- a/include/sqlpp11/core/clause/insert_value_list.h
+++ b/include/sqlpp11/core/clause/insert_value_list.h
@@ -29,7 +29,7 @@
 #include <sqlpp11/core/operator/assign_expression.h>
 #include <sqlpp11/core/basic/column_fwd.h>
 #include <sqlpp11/core/clause/insert_value.h>
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/logic.h>
 #include <sqlpp11/core/no_data.h>
 #include <sqlpp11/core/query/policy_update.h>
@@ -405,7 +405,7 @@ namespace sqlpp
   auto to_sql_string(Context& context, const column_list_data_t<Columns...>& t) -> std::string
   {
     auto result = std::string{" ("};
-    result += interpret_tuple(t._columns, ",", context);
+    result += tuple_to_sql_string(context, t._columns, ",");
     result += ")";
     bool first = true;
     for (const auto& row : t._insert_values)
@@ -420,7 +420,7 @@ namespace sqlpp
         result += ',';
       }
       result += '(';
-      result += interpret_tuple(row, ",", context);
+      result += tuple_to_sql_string(context, row, ",");
       result += ')';
     }
 
@@ -431,9 +431,9 @@ namespace sqlpp
   auto to_sql_string(Context& context, const insert_list_data_t<Assignments...>& t) -> std::string
   {
     auto result = std::string{" ("};
-    result += interpret_tuple(t._columns, ",", context);
+    result += tuple_to_sql_string(context, t._columns, tuple_operand{", "});
     result += ") VALUES(";
-    result += interpret_tuple(t._values, ",", context);
+    result += tuple_to_sql_string(context, t._values, tuple_operand{", "});
     result += ")";
     return result;
   }
diff --git a/include/sqlpp11/core/clause/order_by.h b/include/sqlpp11/core/clause/order_by.h
index 10a4e066..a62e5107 100644
--- a/include/sqlpp11/core/clause/order_by.h
+++ b/include/sqlpp11/core/clause/order_by.h
@@ -27,7 +27,7 @@
  */
 
 #include <sqlpp11/core/detail/type_set.h>
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/logic.h>
 #include <sqlpp11/core/query/policy_update.h>
 #include <sqlpp11/core/type_traits.h>
@@ -148,7 +148,7 @@ namespace sqlpp
   template <typename Context, typename... Expressions>
   auto to_sql_string(Context& context, const order_by_data_t<Expressions...>& t) -> std::string
   {
-    return " ORDER BY " + interpret_tuple(t._expressions, ',', context);
+    return " ORDER BY " + tuple_to_sql_string(context, t._expressions, tuple_operand{", "});
   }
 
   template <typename... T>
diff --git a/include/sqlpp11/core/clause/select_column_list.h b/include/sqlpp11/core/clause/select_column_list.h
index 5ba0aff1..4c2d78a8 100644
--- a/include/sqlpp11/core/clause/select_column_list.h
+++ b/include/sqlpp11/core/clause/select_column_list.h
@@ -30,7 +30,7 @@
 #include <sqlpp11/core/operator/as_expression.h>
 #include <sqlpp11/core/query/dynamic.h>
 #include <sqlpp11/core/field_spec.h>
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/query/policy_update.h>
 #include <sqlpp11/core/query/result_row.h>
 #include <sqlpp11/core/clause/select_as.h>
@@ -330,7 +330,7 @@ namespace sqlpp
   template <typename Context, typename... Columns>
   auto to_sql_string(Context& context, const std::tuple<Columns...>& t) -> std::string
   {
-    return interpret_tuple(t, ",", context);
+    return tuple_to_sql_string(context, t, tuple_operand{", "});
   }
 
   template <typename... T>
diff --git a/include/sqlpp11/core/clause/select_flag_list.h b/include/sqlpp11/core/clause/select_flag_list.h
index ab232d5d..42e76052 100644
--- a/include/sqlpp11/core/clause/select_flag_list.h
+++ b/include/sqlpp11/core/clause/select_flag_list.h
@@ -27,7 +27,7 @@
  */
 
 #include <sqlpp11/core/detail/type_set.h>
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/no_data.h>
 #include <sqlpp11/core/query/policy_update.h>
 #include <sqlpp11/core/clause/select_flags.h>
@@ -137,7 +137,7 @@ namespace sqlpp
   template <typename Context, typename... Flags>
   auto to_sql_string(Context& context, const select_flag_list_data_t<Flags...>& t) -> std::string
   {
-    return interpret_tuple(t._flags, "", context);
+    return tuple_to_sql_string(context, t._flags, tuple_operand{" "});
   }
 
   template <typename T>
diff --git a/include/sqlpp11/core/clause/select_flags.h b/include/sqlpp11/core/clause/select_flags.h
index eaa18143..a446dc3a 100644
--- a/include/sqlpp11/core/clause/select_flags.h
+++ b/include/sqlpp11/core/clause/select_flags.h
@@ -28,7 +28,7 @@
 
 #include <sqlpp11/core/type_traits.h>
 #include <sqlpp11/core/detail/type_set.h>
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <tuple>
 
 namespace sqlpp
diff --git a/include/sqlpp11/core/clause/union.h b/include/sqlpp11/core/clause/union.h
index 5441497a..c8572554 100644
--- a/include/sqlpp11/core/clause/union.h
+++ b/include/sqlpp11/core/clause/union.h
@@ -26,7 +26,7 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/logic.h>
 #include <sqlpp11/core/query/result_row.h>
 #include <sqlpp11/core/query/statement_fwd.h>
diff --git a/include/sqlpp11/core/clause/union_flags.h b/include/sqlpp11/core/clause/union_flags.h
index 07846425..ac334d92 100644
--- a/include/sqlpp11/core/clause/union_flags.h
+++ b/include/sqlpp11/core/clause/union_flags.h
@@ -28,7 +28,7 @@
 
 #include <sqlpp11/core/type_traits.h>
 #include <sqlpp11/core/detail/type_set.h>
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <tuple>
 
 namespace sqlpp
diff --git a/include/sqlpp11/core/clause/update_list.h b/include/sqlpp11/core/clause/update_list.h
index a53903c6..c8eb3a92 100644
--- a/include/sqlpp11/core/clause/update_list.h
+++ b/include/sqlpp11/core/clause/update_list.h
@@ -27,7 +27,7 @@
  */
 
 #include <sqlpp11/core/detail/type_set.h>
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/type_traits.h>
 
 namespace sqlpp
@@ -167,6 +167,6 @@ namespace sqlpp
   template <typename Context, typename... Assignments>
   auto to_sql_string(Context& context, const update_list_data_t<Assignments...>& t) -> std::string
   {
-    return " SET " + interpret_tuple(t._assignments, ",", context);
+    return " SET " + tuple_to_sql_string(context, t._assignments, tuple_operand{", "});
   }
 }  // namespace sqlpp
diff --git a/include/sqlpp11/core/clause/using.h b/include/sqlpp11/core/clause/using.h
index 96b55a16..6e23eec3 100644
--- a/include/sqlpp11/core/clause/using.h
+++ b/include/sqlpp11/core/clause/using.h
@@ -27,7 +27,7 @@
  */
 
 #include <sqlpp11/core/detail/type_set.h>
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/query/policy_update.h>
 #include <sqlpp11/core/type_traits.h>
 
@@ -138,8 +138,6 @@ namespace sqlpp
   template <typename Context, typename... Tables>
   auto to_sql_string(Context& context, const using_data_t<Tables...>& t) -> std::string
   {
-    context << " USING ";
-    interpret_tuple(t._tables, ',', context);
-    return context;
+    return " USING " + tuple_to_sql_string(context, t._tables, tuple_operand{", "});
   }
 }  // namespace sqlpp
diff --git a/include/sqlpp11/core/clause/where.h b/include/sqlpp11/core/clause/where.h
index a37dcdaf..e4715d69 100644
--- a/include/sqlpp11/core/clause/where.h
+++ b/include/sqlpp11/core/clause/where.h
@@ -26,7 +26,7 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/logic.h>
 #include <sqlpp11/core/query/statement_fwd.h>
 #include <sqlpp11/core/type_traits.h>
diff --git a/include/sqlpp11/core/clause/with.h b/include/sqlpp11/core/clause/with.h
index 8cb161c7..a5c03c07 100644
--- a/include/sqlpp11/core/clause/with.h
+++ b/include/sqlpp11/core/clause/with.h
@@ -28,7 +28,7 @@
 
 #include <sqlpp11/core/operator/assign_expression.h>
 #include <sqlpp11/core/basic/column_fwd.h>
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/logic.h>
 #include <sqlpp11/core/no_data.h>
 #include <sqlpp11/core/query/policy_update.h>
@@ -132,7 +132,7 @@ namespace sqlpp
     {
       context << "RECURSIVE ";
     }
-    interpret_tuple(t._expressions, ',', context);
+    tuple_to_sql_string(context, t._expressions, tuple_operand{", "});
     context << ' ';
     return context;
   }
diff --git a/include/sqlpp11/core/database/parameter_list.h b/include/sqlpp11/core/database/parameter_list.h
index 51bead7e..fbfd16b1 100644
--- a/include/sqlpp11/core/database/parameter_list.h
+++ b/include/sqlpp11/core/database/parameter_list.h
@@ -59,7 +59,7 @@ namespace sqlpp
     template <typename Target, size_t... Is>
     void _bind_impl(Target& target, const ::sqlpp::index_sequence<Is...>& /*unused*/) const
     {
-      using swallow = int[];  // see core/interpret_tuple.h
+      using swallow = int[];  // see coretuple_to_sql_string.h
       (void)swallow{0, (std::tuple_element<Is, _member_tuple_t>::type::operator()()._bind(target, Is), 0)...};
     }
   };
diff --git a/include/sqlpp11/core/operator/in_expression.h b/include/sqlpp11/core/operator/in_expression.h
index 47006911..9de5aba2 100644
--- a/include/sqlpp11/core/operator/in_expression.h
+++ b/include/sqlpp11/core/operator/in_expression.h
@@ -32,7 +32,7 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <sqlpp11/core/operator/enable_as.h>
 #include <sqlpp11/core/type_traits.h>
 #include <sqlpp11/core/logic.h>
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 
 namespace sqlpp
 {
@@ -127,8 +127,7 @@ namespace sqlpp
     }
     else
     {
-#warning: interpret_tuple arguments should take Context first, too
-      result += interpret_tuple(t._r, ", ", context);
+      result += tuple_to_sql_string(context, t._r, tuple_operand{", "});
     }
     result += ")";
     return result;
diff --git a/include/sqlpp11/core/query/custom_query.h b/include/sqlpp11/core/query/custom_query.h
index a26d8cf7..d336746a 100644
--- a/include/sqlpp11/core/query/custom_query.h
+++ b/include/sqlpp11/core/query/custom_query.h
@@ -29,7 +29,7 @@
 #include <sqlpp11/core/database/connection.h>
 #include <sqlpp11/core/detail/get_first.h>
 #include <sqlpp11/core/hidden.h>
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/query/statement.h>
 
 namespace sqlpp
@@ -125,7 +125,7 @@ namespace sqlpp
   template <typename Context, typename... Parts>
   auto to_sql_string(Context& context, const custom_query_t<Parts...>& t) -> std::string
   {
-    return interpret_tuple_without_braces(t._parts, " ", context);
+    return tuple_to_sql_string(context, t._parts, tuple_clause{" "});
   }
 
   template <typename... Parts>
diff --git a/include/sqlpp11/core/interpret_tuple.h b/include/sqlpp11/core/tuple_to_sql_string.h
similarity index 52%
rename from include/sqlpp11/core/interpret_tuple.h
rename to include/sqlpp11/core/tuple_to_sql_string.h
index 84ffe8be..41e3902a 100644
--- a/include/sqlpp11/core/interpret_tuple.h
+++ b/include/sqlpp11/core/tuple_to_sql_string.h
@@ -1,7 +1,7 @@
 #pragma once
 
 /*
- * Copyright (c) 2013-2015, Roland Bock
+ * Copyright (c) 2024, Roland Bock
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without modification,
@@ -33,53 +33,80 @@
 
 namespace sqlpp
 {
-  template <typename Element, typename Separator, typename Context, typename UseBraces>
-  static auto interpret_tuple_element(
-      const Element& element, const Separator& separator, Context& context, const UseBraces& /*unused*/, size_t index) -> std::string
+  struct tuple_operand
   {
-    const auto prefix = index ? std::string{separator} : std::string{};
-    if (UseBraces::value)
+    template <typename Context, typename T>
+    auto operator()(Context& context, const T& t, size_t index) const -> std::string
     {
-      return prefix + operand_to_sql_string(context, element);
+      const auto prefix = index ? std::string{separator} : std::string{};
+      return prefix + operand_to_sql_string(context, t);
     }
-    else
-    {
-      return prefix + to_sql_string(context, element);
-    }
-  }
 
-  template <typename Tuple, typename Separator, typename Context, typename UseBraces, size_t... Is>
-  auto interpret_tuple_impl(const Tuple& t,
-                            const Separator& separator,
-                            Context& context,
-                            const UseBraces& useBraces,
-                            const ::sqlpp::index_sequence<Is...> &
-                            /*unused*/) -> std::string
+    sqlpp::string_view separator;
+  };
+
+#warning: to be used by group_by and update
+  struct tuple_operand_no_dynamic
+  {
+    template <typename Context, typename T>
+    auto operator()(Context& context, const T& t, size_t ) const -> std::string
+    {
+      const auto prefix = need_prefix ? std::string{separator} : std::string{};
+      need_prefix = true;
+      return prefix + operand_to_sql_string(context, t);
+    }
+
+    template <typename Context, typename T>
+    auto operator()(Context& context, const sqlpp::dynamic_t<T>& t, size_t index) const -> std::string
+    {
+      if (t._condition)
+      {
+        return operator()(context, t._expr, index);
+      }
+      return "";
+    }
+
+    sqlpp::string_view separator;
+    bool need_prefix = false;
+  };
+
+  struct tuple_clause
+  {
+    template <typename Context, typename T>
+    auto operator()(Context& context, const T& t, size_t index) const -> std::string
+    {
+      const auto prefix = index ? std::string{separator} : std::string{};
+      return prefix + to_sql_string(context, t);
+    }
+
+    sqlpp::string_view separator;
+  };
+
+  template <typename Context, typename Tuple, typename Strategy, size_t... Is>
+  auto tuple_to_sql_string_impl(Context& context,
+                                const Tuple& t,
+                                const Strategy& strategy,
+                                const ::sqlpp::index_sequence<Is...>&
+                                /*unused*/) -> std::string
   {
     // Note: A braced-init-list does guarantee the order of evaluation according to 12.6.1 [class.explicit.init]
     // paragraph 2 and 8.5.4 [dcl.init.list] paragraph 4.
     // See for example: "http://en.cppreference.com/w/cpp/utility/integer_sequence"
     // See also: "http://stackoverflow.com/questions/6245735/pretty-print-stdtuple/6245777#6245777"
     // Beware of gcc-bug: "http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253", otherwise an empty swallow struct could
-    // be used
+    // be used.
     auto result = std::string{};
     using swallow = int[];
     (void)swallow{0,  // workaround against -Wpedantic GCC warning "zero-size array 'int [0]'"
-                  (result += interpret_tuple_element(std::get<Is>(t), separator, context, useBraces, Is), 0)...};
+                  (result += strategy(context, std::get<Is>(t), Is), 0)...};
     return result;
   }
 
-  template <typename Tuple, typename Separator, typename Context>
-  auto interpret_tuple(const Tuple& t, const Separator& separator, Context& context) -> std::string
+  template <typename Context, typename Tuple, typename Strategy>
+  auto tuple_to_sql_string(Context& context, const Tuple& t, const Strategy& strategy) -> std::string
   {
-    return interpret_tuple_impl(t, separator, context, std::true_type{},
+    return tuple_to_sql_string_impl(context, t, strategy,
                                 ::sqlpp::make_index_sequence<std::tuple_size<Tuple>::value>{});
   }
 
-  template <typename Tuple, typename Separator, typename Context>
-  auto interpret_tuple_without_braces(const Tuple& t, const Separator& separator, Context& context) -> std::string
-  {
-    return interpret_tuple_impl(t, separator, context, std::false_type{},
-                                ::sqlpp::make_index_sequence<std::tuple_size<Tuple>::value>{});
-  }
 }  // namespace sqlpp
diff --git a/include/sqlpp11/mysql/serializer.h b/include/sqlpp11/mysql/serializer.h
index 43494c04..83ad42ee 100644
--- a/include/sqlpp11/mysql/serializer.h
+++ b/include/sqlpp11/mysql/serializer.h
@@ -32,17 +32,13 @@
 namespace sqlpp
 {
   template <typename First, typename... Args>
-  mysql::context_t& to_sql_string(const concat_t<First, Args...>& t, mysql::context_t& ctx)
+  auto to_sql_string(mysql::context_t& ctx, const concat_t<First, Args...>& t, mysql::context_t& ctx) -> std::string
   {
-    ctx << "CONCAT(";
-    interpret_tuple(t._args, ',', ctx);
-    ctx << ')';
-    return ctx;
+    return "CONCAT(" + tuple_to_sql_string(context, t._args, tuple_operand(", ")) + ")";
   }
 
-  inline mysql::context_t& to_sql_string(const insert_default_values_data_t&, mysql::context_t& ctx)
+  inline auto to_sql_string(mysql::context_t&, const insert_default_values_data_t&) -> std::string
   {
-    ctx << " () VALUES()";
-    return ctx;
+    return " () VALUES()";
   }
 }
diff --git a/include/sqlpp11/postgresql/on_conflict_do_update.h b/include/sqlpp11/postgresql/on_conflict_do_update.h
index 813235ed..ef287f2e 100644
--- a/include/sqlpp11/postgresql/on_conflict_do_update.h
+++ b/include/sqlpp11/postgresql/on_conflict_do_update.h
@@ -28,7 +28,7 @@
  */
 
 #include <sqlpp11/core/detail/type_set.h>
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/type_traits.h>
 #include <sqlpp11/core/clause/where.h>
 
@@ -139,14 +139,10 @@ namespace sqlpp
     };
 
     template <typename ConflictTarget, typename... Assignments>
-    postgresql::context_t& to_sql_string(
-        const postgresql::on_conflict_do_update_data_t<ConflictTarget, Assignments...>& o,
-        postgresql::context_t& context)
+    auto to_sql_string(postgresql::context_t& context,
+        const postgresql::on_conflict_do_update_data_t<ConflictTarget, Assignments...>& o) -> std::string
     {
-      to_sql_string(context, o._conflict_target);
-      context << "DO UPDATE SET ";
-      interpret_tuple(o._assignments, ",", context);
-      return context;
+      return to_sql_string(context, o._conflict_target) + "DO UPDATE SET " + tuple_to_sql_string(context, o._assignments, tuple_operand{", "});
     }
 
     template <typename ConflictTarget, typename Expression, typename... Assignments>
diff --git a/include/sqlpp11/postgresql/returning_column_list.h b/include/sqlpp11/postgresql/returning_column_list.h
index 7cd28bc7..ad2ff468 100644
--- a/include/sqlpp11/postgresql/returning_column_list.h
+++ b/include/sqlpp11/postgresql/returning_column_list.h
@@ -32,7 +32,7 @@
 #include <sqlpp11/core/detail/type_set.h>
 #include <sqlpp11/expression_fwd.h>
 #include <sqlpp11/core/field_spec.h>
-#include <sqlpp11/core/interpret_tuple.h>
+#include <sqlpp11/core/tuple_to_sql_string.h>
 #include <sqlpp11/core/query/policy_update.h>
 #include <sqlpp11/core/query/result_row.h>
 #include <sqlpp11/select_pseudo_table.h>
@@ -293,12 +293,9 @@ namespace sqlpp
 
     // Serialization
     template <typename... Columns>
-    postgresql::context_t& to_sql_string(const postgresql::returning_column_list_data_t<Columns...>& t,
-                                     postgresql::context_t& context)
+    auto to_sql_string(postgresql::context_t& context, const postgresql::returning_column_list_data_t<Columns...>& t) -> std::string
     {
-      context << " RETURNING ";
-      interpret_tuple(t._columns, ',', context);
-      return context;
+      return " RETURNING " +  tuple_to_sql_string(context, t._columns, tuple_operand{", "});
     }
   }
 }  // namespace sqlpp