From b3229d48b7595969f8ec82cfb5ee89f788248f2c Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Sat, 11 Jan 2020 05:27:57 +0200
Subject: [PATCH] gcc < 7 doesn't like specializing std::hash in a different
 namespace

---
 include/boost/variant2/variant.hpp | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/boost/variant2/variant.hpp b/include/boost/variant2/variant.hpp
index df78adf..e99382c 100644
--- a/include/boost/variant2/variant.hpp
+++ b/include/boost/variant2/variant.hpp
@@ -1855,18 +1855,23 @@ template<class V> struct std_hash_impl<V, true>
 } // namespace variant2
 } // namespace boost
 
-template<class... T> struct std::hash< boost::variant2::variant<T...> >: public boost::variant2::detail::std_hash_impl< boost::variant2::variant<T...> >
+namespace std
+{
+
+template<class... T> struct hash< ::boost::variant2::variant<T...> >: public ::boost::variant2::detail::std_hash_impl< ::boost::variant2::variant<T...> >
 {
 };
 
-template<> struct std::hash< boost::variant2::monostate >
+template<> struct hash< ::boost::variant2::monostate >
 {
-    std::size_t operator()( boost::variant2::monostate const & v ) const
+    std::size_t operator()( ::boost::variant2::monostate const & v ) const
     {
         return hash_value( v );
     }
 };
 
+} // namespace std
+
 #if defined(_MSC_VER) && _MSC_VER < 1910
 # pragma warning( pop )
 #endif