Add generic version of has_nothrow_assign.

Does not require a compiler intrinsic - makes it easier to port to other/unknown compilers going forward as long as they are C++11.

include/boost/type_traits/detail/decl.hpp

@@ -0,0 +1,29 @@
+
+//  (C) Copyright John Maddock 2015.
+//  Use, modification and distribution are subject to the Boost Software License,
+//  Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt).
+//
+//  See http://www.boost.org/libs/type_traits for most recent version including documentation.
+
+#ifndef BOOST_TT_DETAIL_DECL_HEADER
+#define BOOST_TT_DETAIL_DECL_HEADER
+
+#include <boost/config.hpp>
+#include <boost/type_traits/add_rvalue_reference.hpp>
+#include <boost/type_traits/add_lvalue_reference.hpp>
+#include <boost/type_traits/remove_reference.hpp>
+
+namespace boost { namespace detail{
+
+template <typename T>
+typename add_rvalue_reference<T>::type tt_declval() BOOST_NOEXCEPT; // as unevaluated operand
+template <typename T>
+typename add_lvalue_reference<typename remove_reference<T>::type const>::type tt_decl_const_ref() BOOST_NOEXCEPT; // as unevaluated operand
+template <typename T>
+typename add_lvalue_reference<typename remove_reference<T>::type>::type tt_decl_ref() BOOST_NOEXCEPT; // as unevaluated operand
+
+
+}} // namespace boost
+
+#endif // BOOST_TT_DETAIL_DECL_HEADER

include/boost/type_traits/has_nothrow_assign.hpp

@@ -14,6 +14,12 @@
 
 #if !defined(BOOST_HAS_NOTHROW_ASSIGN) || defined(BOOST_MSVC) || defined(BOOST_INTEL)
 #include <boost/type_traits/has_trivial_assign.hpp>
+#if !defined(BOOST_NO_CXX11_NOEXCEPT) && !defined(BOOST_NO_SFINAE_EXPR) && !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+#include <boost/type_traits/detail/decl.hpp>
+#include <boost/type_traits/is_const.hpp>
+#include <boost/type_traits/is_volatile.hpp>
+#include <boost/type_traits/is_reference.hpp>
+#endif
 #endif
 #if defined(__GNUC__) || defined(__SUNPRO_CC)
 #include <boost/type_traits/is_const.hpp>
@@ -25,10 +31,27 @@
 
 namespace boost {
 
+#if !defined(BOOST_HAS_NOTHROW_ASSIGN) && !defined(BOOST_NO_CXX11_NOEXCEPT) && !defined(BOOST_NO_SFINAE_EXPR) && !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+
+   namespace detail
+   {
+      template <class T, bool b1> struct has_nothrow_assign_imp{ static const bool value = false; };
+      template <class T>          struct has_nothrow_assign_imp<T, false>{ static const bool value = noexcept(detail::tt_decl_ref<T>() = detail::tt_decl_const_ref<T>()); };
+      template <class T, std::size_t N> struct has_nothrow_assign_imp<T[N], false>{ static const bool value = has_nothrow_assign_imp<T, false>::value; };
+      template <class T>          struct has_nothrow_assign_imp<T[], false>{ static const bool value = has_nothrow_assign_imp<T, false>::value; };
+   }
+
+#endif
+
 template <class T>
 struct has_nothrow_assign : public integral_constant<bool,
 #ifndef BOOST_HAS_NOTHROW_ASSIGN
+#if !defined(BOOST_NO_CXX11_NOEXCEPT) && !defined(BOOST_NO_SFINAE_EXPR) && !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+   // Portable C++11 version:
+   detail::has_nothrow_assign_imp<T, is_const<typename remove_reference<T>::type>::value || is_volatile<typename remove_reference<T>::type>::value || is_reference<T>::value>::value
+#else
    ::boost::has_trivial_assign<T>::value
+#endif
 #else
    BOOST_HAS_NOTHROW_ASSIGN(T)
 #endif

test/Jamfile.v2

@@ -29,6 +29,10 @@ rule all-tests {
      {
          result += [ run $(source) ] ;
      }
+     for local source in has_nothrow_assign_test
+     {
+         result += [ run $(source).cpp : : : <define>BOOST_TT_DISABLE_INTRINSICS : $(source)_no_intrinsics ] ;
+     }
      return $(result) ;     
 }