utils: Use BOOST_CLASS_IMPLEMENTATION on Array/Vector

Change the Boost serialization object class info to elide two
short ints (version for Utils::detail::Storage and Utils::Array),
thus reducing the serialization buffer size by 25% for Vector3i
(from 16 to 12 bytes) and by 14% for Vector3d (from 28 to 24 bytes).

src/utils/include/utils/Array.hpp

@@ -21,6 +21,7 @@
 
 #include "device_qualifier.hpp"
 #include "get.hpp"
+#include "serialization/array.hpp"
 
 #include <boost/serialization/access.hpp>
 #include <boost/serialization/array_wrapper.hpp>
@@ -210,4 +211,8 @@ auto get(Array<T, N> const &a) -> std::enable_if_t<(I < N), const T &> {
 }
 
 } // namespace Utils
+
+UTILS_ARRAY_BOOST_CLASS(Utils::detail::Storage, N, object_serializable)
+UTILS_ARRAY_BOOST_CLASS(Utils::Array, N, object_serializable)
+
 #endif

src/utils/include/utils/Vector.hpp

@@ -500,4 +500,7 @@ template <typename T> struct deduce_vec<Utils::Vector<T, 3>, 3> {
 
 } // namespace qvm
 } // namespace boost
+
+UTILS_ARRAY_BOOST_CLASS(Utils::Vector, N, object_serializable)
+
 #endif

src/utils/include/utils/serialization/array.hpp

@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2021 The ESPResSo project
+ *
+ * This file is part of ESPResSo.
+ *
+ * ESPResSo is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * ESPResSo is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef UTILS_SERIALIZATION_ARRAY_HPP
+#define UTILS_SERIALIZATION_ARRAY_HPP
+
+#include <boost/mpl/int.hpp>
+#include <boost/mpl/integral_c_tag.hpp>
+#include <boost/serialization/level.hpp>
+
+#include <cstddef>
+
+#define UTILS_ARRAY_TEMPLATE_T_N template <typename T, std::size_t N>
+#define UTILS_ARRAY_TEMPLATE_T_0 template <typename T>
+#define UTILS_ARRAY_CONTAINER_T_N(Container) Container<T, N>
+#define UTILS_ARRAY_CONTAINER_T_0(Container) Container<T>
+
+/**
+ * @brief Redefinition of @c BOOST_CLASS_IMPLEMENTATION for array types.
+ * @tparam Container            Template template type of the array
+ * @tparam N                    N if @p Container uses std::size_t N, else 0
+ * @tparam ImplementationLevel  Serialization implementation level
+ */
+#define UTILS_ARRAY_BOOST_CLASS(Container, N, ImplementationLevel)             \
+  namespace boost {                                                            \
+  namespace serialization {                                                    \
+  UTILS_ARRAY_TEMPLATE_T_##N struct implementation_level_impl<                 \
+      const UTILS_ARRAY_CONTAINER_T_##N(Container)> {                          \
+    typedef mpl::integral_c_tag tag;                                           \
+    typedef mpl::int_<ImplementationLevel> type;                               \
+    BOOST_STATIC_CONSTANT(int,                                                 \
+                          value = implementation_level_impl::type::value);     \
+  };                                                                           \
+  } /* namespace serialization */                                              \
+  } /* namespace boost */
+
+#endif