update boost

linx64/include/boost/histogram/detail/variant_proxy.hpp

@@ -0,0 +1,67 @@
+// Copyright 2019 Hans Dembinski
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt
+// or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_HISTOGRAM_DETAIL_VARIANT_PROXY_HPP
+#define BOOST_HISTOGRAM_DETAIL_VARIANT_PROXY_HPP
+
+#include <boost/core/nvp.hpp>
+#include <boost/histogram/axis/traits.hpp> // variant_access
+#include <boost/histogram/detail/static_if.hpp>
+#include <boost/mp11/algorithm.hpp> // mp_with_index, mp_find, mp_at
+#include <boost/mp11/list.hpp>      // mp_size
+#include <boost/throw_exception.hpp>
+#include <stdexcept>
+
+namespace boost {
+namespace histogram {
+namespace detail {
+
+// This is a workaround to remain backward compatible in the serialization format. The
+// proxy uses only the public interface of axis::variant for serialization and works
+// independently of the underlying variant implementation.
+template <class Variant>
+struct variant_proxy {
+  Variant& variant;
+
+  template <class Archive>
+  void serialize(Archive& ar, unsigned /* version */) {
+    detail::static_if_c<Archive::is_loading::value>(
+        [this](auto& ar) { // loading
+          int which = 0;
+          ar >> make_nvp("which", which);
+          constexpr unsigned N = mp11::mp_size<Variant>::value;
+          if (which < 0 || static_cast<unsigned>(which) >= N)
+            // throw if which >= N, can happen if type was removed from variant
+            BOOST_THROW_EXCEPTION(
+                std::runtime_error("variant has fewer types than stored version"));
+          mp11::mp_with_index<N>(static_cast<unsigned>(which), [&ar, this](auto i) {
+            using T = mp11::mp_at_c<Variant, i>;
+            T value;
+            ar >> make_nvp("value", value);
+            this->variant = std::move(value);
+            T* new_address = variant_access::template get_if<T>(&this->variant);
+            ar.reset_object_address(new_address, &value);
+          });
+        },
+        [this](auto& ar) { // saving
+          visit(
+              [&ar](const auto& value) {
+                using T = std::decay_t<decltype(value)>;
+                const int which = static_cast<int>(mp11::mp_find<Variant, T>::value);
+                ar << make_nvp("which", which);
+                ar << make_nvp("value", value);
+              },
+              this->variant);
+        },
+        ar);
+  }
+};
+
+} // namespace detail
+} // namespace histogram
+} // namespace boost
+
+#endif