Add support for value wrappers

Wrapper is a class that wraps another type. Examples of wrappers are
various smart pointers, holders, etc. A wrapper can be transparent or
it can handle the NULL semantics.

The new odb::nullable class template is a NULL wrapper that helps
to add the NULL semantics to a value type.

New test: common/wrapper.

1 files changed, 16 insertions, 0 deletions

diff --git a/query/person.hxx b/query/person.hxx
index 72da079..db312f2 100644
--- a/query/person.hxx
+++ b/query/person.hxx
@@ -8,6 +8,7 @@
 #include <string>
 
 #include <odb/core.hxx>
+#include <odb/nullable.hxx>
 
 #pragma db object
 class person
@@ -20,12 +21,26 @@ public:
   {
   }
 
+  person (const std::string& first,
+          const std::string& middle,
+          const std::string& last,
+          unsigned short age)
+      : first_ (first), middle_ (middle), last_ (last), age_ (age)
+  {
+  }
+
   const std::string&
   first () const
   {
     return first_;
   }
 
+  const odb::nullable<std::string>&
+  middle () const
+  {
+    return middle_;
+  }
+
   const std::string&
   last () const
   {
@@ -47,6 +62,7 @@ private:
   unsigned long id_;
 
   std::string first_;
+  odb::nullable<std::string> middle_;
   std::string last_;
   unsigned short age_;
 };