From c1287f9e957692f58aa3bb2166d7ce5f429b511a Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Thu, 21 Feb 2019 23:06:24 +0200
Subject: [PATCH] Fix variant_alternative for g++ 4.8

---
 include/boost/variant2/variant.hpp | 48 ++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/include/boost/variant2/variant.hpp b/include/boost/variant2/variant.hpp
index 23ce723..8cb7ad8 100644
--- a/include/boost/variant2/variant.hpp
+++ b/include/boost/variant2/variant.hpp
@@ -137,10 +137,34 @@ template<std::size_t I, class... T> struct variant_alternative_impl<I, variant<T
 {
 };
 
+template<std::size_t I, class... T> struct variant_alternative_impl<I, variant<T...> const&, true>: std::add_lvalue_reference< mp11::mp_at_c<variant<T...>, I> const >
+{
+};
+
+template<std::size_t I, class... T> struct variant_alternative_impl<I, variant<T...> volatile&, true>: std::add_lvalue_reference< mp11::mp_at_c<variant<T...>, I> volatile >
+{
+};
+
+template<std::size_t I, class... T> struct variant_alternative_impl<I, variant<T...> const volatile&, true>: std::add_lvalue_reference< mp11::mp_at_c<variant<T...>, I> const volatile >
+{
+};
+
 template<std::size_t I, class... T> struct variant_alternative_impl<I, variant<T...>&&, true>: std::add_rvalue_reference< mp11::mp_at_c<variant<T...>, I> >
 {
 };
 
+template<std::size_t I, class... T> struct variant_alternative_impl<I, variant<T...> const&&, true>: std::add_rvalue_reference< mp11::mp_at_c<variant<T...>, I> const >
+{
+};
+
+template<std::size_t I, class... T> struct variant_alternative_impl<I, variant<T...> volatile&&, true>: std::add_rvalue_reference< mp11::mp_at_c<variant<T...>, I> volatile >
+{
+};
+
+template<std::size_t I, class... T> struct variant_alternative_impl<I, variant<T...> const volatile&&, true>: std::add_rvalue_reference< mp11::mp_at_c<variant<T...>, I> const volatile >
+{
+};
+
 } // namespace detail
 
 template<std::size_t I, class T> struct variant_alternative
@@ -167,10 +191,34 @@ template<std::size_t I, class... T> struct variant_alternative<I, variant<T...>&
 {
 };
 
+template<std::size_t I, class... T> struct variant_alternative<I, variant<T...> const&>: public detail::variant_alternative_impl<I, variant<T...> const&, (I < sizeof...(T))>
+{
+};
+
+template<std::size_t I, class... T> struct variant_alternative<I, variant<T...> volatile&>: public detail::variant_alternative_impl<I, variant<T...> volatile&, (I < sizeof...(T))>
+{
+};
+
+template<std::size_t I, class... T> struct variant_alternative<I, variant<T...> const volatile&>: public detail::variant_alternative_impl<I, variant<T...> const volatile&, (I < sizeof...(T))>
+{
+};
+
 template<std::size_t I, class... T> struct variant_alternative<I, variant<T...>&&>: public detail::variant_alternative_impl<I, variant<T...>&&, (I < sizeof...(T))>
 {
 };
 
+template<std::size_t I, class... T> struct variant_alternative<I, variant<T...> const&&>: public detail::variant_alternative_impl<I, variant<T...> const&&, (I < sizeof...(T))>
+{
+};
+
+template<std::size_t I, class... T> struct variant_alternative<I, variant<T...> volatile&&>: public detail::variant_alternative_impl<I, variant<T...> volatile&&, (I < sizeof...(T))>
+{
+};
+
+template<std::size_t I, class... T> struct variant_alternative<I, variant<T...> const volatile&&>: public detail::variant_alternative_impl<I, variant<T...> const volatile&&, (I < sizeof...(T))>
+{
+};
+
 #else
 
 namespace detail