added sql function and alias

include/matador/sql/query_result.hpp

@@ -105,6 +105,19 @@ private:
   query_result<Type> *result_{nullptr};
 };
 
+namespace detail {
+
+template < typename Type >
+Type* create_prototype(const record &/*prototype*/)
+{
+  return new Type{};
+}
+
+template <>
+record* create_prototype<record>(const record &prototype);
+
+}
+
 template < typename Type >
 class query_result
 {
@@ -116,8 +129,8 @@ public:
   explicit query_result(std::unique_ptr<query_result_impl> impl)
   : impl_(std::move(impl)) {}
 
-  query_result(std::unique_ptr<query_result_impl> impl, creator_func creator)
-  : creator_(creator)
+  query_result(std::unique_ptr<query_result_impl> impl, record record_prototype)
+  : record_prototype_(std::move(record_prototype))
   , impl_(std::move(impl)) {}
 
   iterator begin() { return std::move(++iterator(this)); }
@@ -126,7 +139,7 @@ public:
 private:
   friend class query_result_iterator<Type>;
 
-  Type* create() { return creator_(); }
+  Type* create() { return detail::create_prototype<Type>(record_prototype_); }
 
   void bind(const Type &obj)
   {
@@ -139,7 +152,7 @@ private:
   }
 
 private:
-  creator_func creator_ = []{ return new Type; };
+  record record_prototype_;
   std::unique_ptr<query_result_impl> impl_;
 };