From 455e6129bec2a8d56858a189c32af15991efe8db Mon Sep 17 00:00:00 2001
From: Andrey Semashev <andrey.semashev@gmail.com>
Date: Tue, 19 Sep 2017 14:51:45 +0300
Subject: [PATCH] Added a workaround for clang 3.0 not supporting decltype in
 base class list.

Use an additional proxy class to define the base class using decltype in a
typedef, which is supported by the compiler, judging by Boost.Config tests.
---
 include/boost/type_traits/is_nothrow_swappable.hpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/boost/type_traits/is_nothrow_swappable.hpp b/include/boost/type_traits/is_nothrow_swappable.hpp
index b355664..397f296 100644
--- a/include/boost/type_traits/is_nothrow_swappable.hpp
+++ b/include/boost/type_traits/is_nothrow_swappable.hpp
@@ -26,17 +26,21 @@ using std::swap;
 
 template<class T, class U, bool B = noexcept(swap(declval<T>(), declval<U>()))> integral_constant<bool, B> is_nothrow_swappable_with_impl( int );
 template<class T, class U> false_type is_nothrow_swappable_with_impl( ... );
+template<class T, class U>
+struct is_nothrow_swappable_with_helper { typedef decltype( type_traits_swappable_detail::is_nothrow_swappable_with_impl<T, U>(0) ) type; };
 
 template<class T, bool B = noexcept(swap(declval<T&>(), declval<T&>()))> integral_constant<bool, B> is_nothrow_swappable_impl( int );
 template<class T> false_type is_nothrow_swappable_impl( ... );
+template<class T>
+struct is_nothrow_swappable_helper { typedef decltype( type_traits_swappable_detail::is_nothrow_swappable_impl<T>(0) ) type; };
 
 } // namespace type_traits_swappable_detail
 
-template<class T, class U> struct is_nothrow_swappable_with: decltype( type_traits_swappable_detail::is_nothrow_swappable_with_impl<T, U>(0) )
+template<class T, class U> struct is_nothrow_swappable_with: type_traits_swappable_detail::is_nothrow_swappable_with_helper<T, U>::type
 {
 };
 
-template<class T> struct is_nothrow_swappable: decltype( type_traits_swappable_detail::is_nothrow_swappable_impl<T>(0) )
+template<class T> struct is_nothrow_swappable: type_traits_swappable_detail::is_nothrow_swappable_helper<T>::type
 {
 };