Imported Upstream version 1.72.0

[platform/upstream/boost.git] / boost / histogram / fwd.hpp

diff --git a/boost/histogram/fwd.hpp b/boost/histogram/fwd.hpp
index cc042bb..130860a 100644 (file)
--- a/boost/histogram/fwd.hpp
+++ b/boost/histogram/fwd.hpp
@@ -12,8 +12,8 @@
   Forward declarations, tag types and type aliases.
 */
 
+#include <boost/config.hpp> // BOOST_ATTRIBUTE_NODISCARD
 #include <boost/core/use_default.hpp>
-#include <boost/histogram/detail/attribute.hpp> // BOOST_HISTOGRAM_NODISCARD
 #include <vector>
 
 namespace boost {
@@ -31,7 +31,13 @@ using index_type = int;
 using real_index_type = double;
 
 /// Empty metadata type
-struct null_type {};
+struct null_type {
+  template <class Archive>
+  void serialize(Archive&, unsigned /* version */) {}
+};
+
+/// Another alias for an empty metadata type
+using empty_type = null_type;
 
 #ifndef BOOST_HISTOGRAM_DOXYGEN_INVOKED
 
@@ -120,7 +126,7 @@ using weighted_profile_storage = dense_storage<accumulators::weighted_mean<>>;
 #ifndef BOOST_HISTOGRAM_DOXYGEN_INVOKED
 
 template <class Axes, class Storage = default_storage>
-class BOOST_HISTOGRAM_NODISCARD histogram;
+class BOOST_ATTRIBUTE_NODISCARD histogram;
 
 #endif
 } // namespace histogram