From b7ad896707af20a06110b23edfd60a977af47fe1 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Tue, 7 Aug 2018 22:59:25 +0300
Subject: [PATCH] explicit_operator_bool: under g++ 4.6 the operator can't be
 constexpr

---
 include/boost/core/explicit_operator_bool.hpp | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/boost/core/explicit_operator_bool.hpp b/include/boost/core/explicit_operator_bool.hpp
index a8936e2..4660d6a 100644
--- a/include/boost/core/explicit_operator_bool.hpp
+++ b/include/boost/core/explicit_operator_bool.hpp
@@ -19,6 +19,7 @@
 #define BOOST_CORE_EXPLICIT_OPERATOR_BOOL_HPP
 
 #include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
 
 #ifdef BOOST_HAS_PRAGMA_ONCE
 #pragma once
@@ -121,12 +122,20 @@ namespace detail {
         return (!this->operator! () ? &boost::detail::unspecified_bool::true_value : (boost::detail::unspecified_bool_type)0);\
     }
 
+#if BOOST_WORKAROUND(BOOST_GCC_VERSION, < 40700)
+
+#define BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL() BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT()
+
+#else
+
 #define BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL()\
     BOOST_FORCEINLINE BOOST_CONSTEXPR operator boost::detail::unspecified_bool_type () const BOOST_NOEXCEPT\
     {\
         return (!this->operator! () ? &boost::detail::unspecified_bool::true_value : (boost::detail::unspecified_bool_type)0);\
     }
 
+#endif
+
 #else // !defined(BOOST_NO_UNSPECIFIED_BOOL)
 
 #define BOOST_EXPLICIT_OPERATOR_BOOL()\