adding version macro for boost transition layer

.gitignore

@@ -23,6 +23,7 @@
 *.log
 *.tlog*
 
+# misc files mostly used for testing
 out.txt
 ptr.txt
 test.txt
@@ -30,9 +31,9 @@ unittests
 boost_serialize
 arr.txt
 performance
-./sandbox
-./sandbox_rtti
-./sandbox_json
+sandbox
+sandbox_json
+sandbox_rtti
 include_renamed
 .ycm_extra_conf.py*
 doc/html

include/cereal/cereal.hpp

@@ -384,6 +384,9 @@ namespace cereal
 
       //! The id to be given to the next polymorphic type name
       std::uint32_t itsCurrentPolymorphicTypeId;
+
+      //! Keeps track of classes that have versioning information associated with them
+      std::unordered_set<size_type> itsVersionedTypes;
   }; // class OutputArchive
 
   // ######################################################################

include/cereal/details/helpers.hpp

@@ -36,7 +36,6 @@
 
 namespace cereal
 {
-
   //! The size type used by cereal
   /*! To ensure compatability between 32, 64, etc bit machines, we need to use
    * a fixed size type instead of size_t, which may vary from machine to
@@ -305,6 +304,16 @@ namespace cereal
   {
     return {std::forward<KeyType>(key), std::forward<ValueType>(value)};
   }
+
+  //! Defines a class version for some type
+  /*! This is part of the Boost Transition Layer and is not the recommended way
+      of using cereal.  This works identically to how it does in Boost serialization,
+      providing a version number associated with some type that is available by specifying
+      a second parameter to serialize, save, or load. */
+  #define CEREAL_CLASS_VERSION(TYPE, VERSION_NUMBER)                                          \
+  namespace cereal { namespace detail {                                                       \
+    template <> struct Version<TYPE> { static const std::uint32_t version = VERSION_NUMBER; };\
+  } } // end namespaces
 } // namespace cereal
 
 #endif // CEREAL_DETAILS_HELPERS_HPP_

include/cereal/details/traits.hpp

@@ -316,7 +316,6 @@ namespace cereal
       struct base_class_id_hash { size_t operator()(base_class_id const & id) const { return id.hash; }  };
     } // namespace detail
 
-
     // ######################################################################
     //! A macro to use to restrict which types of archives your function will work for.
     /*! This requires you to have a template class parameter named Archive and replaces the void return
@@ -388,6 +387,9 @@ namespace cereal
         return LoadAndAllocate<T>::load_and_allocate( ar );
       }
     };
+
+    //! Version information class - used in Boost Transition Layer
+    template <class T> struct Version;
   } // namespace detail
 } // namespace cereal
 

sandbox.cpp

@@ -656,3 +656,5 @@ int main()
 
   return 0;
 }
+
+CEREAL_CLASS_VERSION(std::vector<int>, 1);