From fbc50bfd1237da7c428257c52362b1ae234fb475 Mon Sep 17 00:00:00 2001
From: John Maddock <john@johnmaddock.co.uk>
Date: Thu, 10 May 2018 11:34:02 +0100
Subject: [PATCH] is_virtual_base_of: more workarounds for clang and older gcc
 versions

---
 include/boost/type_traits/is_virtual_base_of.hpp | 5 +++--
 test/is_virtual_base_of_test.cpp                 | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/boost/type_traits/is_virtual_base_of.hpp b/include/boost/type_traits/is_virtual_base_of.hpp
index cf890b9..f9e1331 100644
--- a/include/boost/type_traits/is_virtual_base_of.hpp
+++ b/include/boost/type_traits/is_virtual_base_of.hpp
@@ -12,6 +12,7 @@
 #include <boost/type_traits/is_base_of.hpp>
 #include <boost/type_traits/is_same.hpp>
 #include <boost/type_traits/make_void.hpp>
+#include <utility>
 
 namespace boost {
    namespace detail {
@@ -24,7 +25,7 @@ namespace boost {
 #pragma GCC system_header
 #endif
 
-#if !defined(BOOST_NO_SFINAE_EXPR) && !defined(BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS) && !defined(BOOST_NO_CXX11_NULLPTR) && !BOOST_WORKAROUND(BOOST_GCC, <= 40800)
+#if !defined(BOOST_NO_SFINAE_EXPR) && !defined(BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS) && !defined(BOOST_NO_CXX11_NULLPTR) && !BOOST_WORKAROUND(BOOST_GCC, < 40800)
 
 #ifdef __clang__
 
@@ -32,7 +33,7 @@ namespace boost {
       constexpr bool is_virtual_base_impl(...) { return true; }
 
       template<class T, class U,
-         boost::void_t<decltype(static_cast<U*>(std::declval<T*>()))>* =
+         boost::void_t<decltype((U*)(std::declval<T*>()))>* =
          nullptr>
          constexpr bool is_virtual_base_impl(int) { return false; }
 
diff --git a/test/is_virtual_base_of_test.cpp b/test/is_virtual_base_of_test.cpp
index aa6435c..4b77b45 100644
--- a/test/is_virtual_base_of_test.cpp
+++ b/test/is_virtual_base_of_test.cpp
@@ -132,7 +132,7 @@ BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<non_virtual_base,non_vir
 //
 BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<bug11309_A, bug11309_C>::value), false);
 BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<bug11309_A, bug11309_B>::value), true);
-#if !defined(BOOST_NO_SFINAE_EXPR) && !defined(BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS) && !defined(BOOST_NO_CXX11_NULLPTR)
+#if !defined(BOOST_NO_SFINAE_EXPR) && !defined(BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS) && !defined(BOOST_NO_CXX11_NULLPTR) && !BOOST_WORKAROUND(BOOST_GCC, < 40800)
 BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<bug11323_B, bug11323_C>::value), false);
 #ifndef BOOST_NO_CXX11_FINAL
 BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_virtual_base_of<bug11323_2B, bug11323_2C>::value), false);