Make fusion::pair trivially copyable if possible

include/boost/fusion/support/pair.hpp

@@ -8,15 +8,16 @@
 #if !defined(FUSION_PAIR_07222005_1203)
 #define FUSION_PAIR_07222005_1203
 
-#include <boost/fusion/support/config.hpp>
 #include <iosfwd>
-
+#include <utility>
+#include <boost/fusion/support/config.hpp>
 #include <boost/fusion/support/detail/access.hpp>
 #include <boost/fusion/support/detail/as_fusion_element.hpp>
-#include <boost/config.hpp>
+#include <boost/fusion/support/detail/enabler.hpp>
-#include <boost/utility/enable_if.hpp>
+#include <boost/core/enable_if.hpp>
+#include <boost/type_traits/is_same.hpp>
 #include <boost/type_traits/is_convertible.hpp>
-#include <boost/type_traits/is_lvalue_reference.hpp>
+#include <boost/type_traits/remove_cv_ref.hpp>
 
 #if defined (BOOST_MSVC)
 #  pragma warning(push)
@@ -33,54 +34,46 @@ namespace boost { namespace fusion
         pair()
             : second() {}
 
-        BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
-        pair(pair const& rhs)
-            : second(rhs.second) {}
-
-#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
-        BOOST_CXX14_CONSTEXPR BOOST_FUSION_GPU_ENABLED
-        pair(pair&& rhs)
-            : second(BOOST_FUSION_FWD_ELEM(Second, rhs.second)) {}
-#endif
-
         BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
         pair(typename detail::call_param<Second>::type val)
             : second(val) {}
 
 #if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
-        template <typename Second2>
         BOOST_FUSION_GPU_ENABLED
-        pair(Second2&& val
+        pair(typename remove_cv_ref<Second>::type&& val)
-          , typename boost::disable_if<is_lvalue_reference<Second2> >::type* /* dummy */ = 0
+            : second(BOOST_FUSION_FWD_ELEM(Second, val)) {}
-          , typename boost::enable_if<is_convertible<Second2, Second> >::type* /*dummy*/ = 0
-        ) : second(BOOST_FUSION_FWD_ELEM(Second, val)) {}
 #endif
 
         template <typename Second2>
         BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
-        pair(pair<First, Second2> const& rhs)
+        pair(pair<First, Second2> const& rhs,
+             typename disable_if<is_same<Second, Second2>, detail::enabler_>::type = detail::enabler,
+             typename enable_if<is_convertible<Second2, Second>, detail::enabler_>::type = detail::enabler)
             : second(rhs.second) {}
 
         template <typename Second2>
         BOOST_CXX14_CONSTEXPR BOOST_FUSION_GPU_ENABLED
-        pair& operator=(pair<First, Second2> const& rhs)
+        typename disable_if<is_same<Second, Second2>, pair&>::type
-        {
+        operator=(pair<First, Second2> const& rhs)
-            second = rhs.second;
-            return *this;
-        }
-
-        BOOST_CXX14_CONSTEXPR BOOST_FUSION_GPU_ENABLED
-        pair& operator=(pair const& rhs)
         {
             second = rhs.second;
             return *this;
         }
 
 #if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+        template <typename Second2>
+        BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+        pair(pair<First, Second2>&& rhs,
+             typename disable_if<is_same<Second, Second2>, detail::enabler_>::type = detail::enabler,
+             typename enable_if<is_convertible<Second2, Second>, detail::enabler_>::type = detail::enabler)
+            : second(std::move(rhs.second)) {}
+
+        template <typename Second2>
         BOOST_CXX14_CONSTEXPR BOOST_FUSION_GPU_ENABLED
-        pair& operator=(pair&& rhs)
+        typename disable_if<is_same<Second, Second2>, pair&>::type
+        operator=(pair<First, Second2>&& rhs)
         {
-            second = BOOST_FUSION_FWD_ELEM(Second, rhs.second);
+            second = std::move(rhs.second);
             return *this;
         }
 #endif

test/Jamfile

@@ -255,6 +255,7 @@ project
     [ run sequence/swap.cpp ]
 
     [ compile support/is_sequence.cpp ]
+    [ compile support/pair_conversion.cpp ]
     [ compile support/pair_deque.cpp ]
     [ compile support/pair_list.cpp ]
     [ compile support/pair_map.cpp ]
@@ -266,6 +267,8 @@ project
     [ compile support/and.cpp
         : [ requires cxx11_variadic_templates ] ]
     [ compile support/tag_of.cpp ]
+    [ compile support/pair_trivially_copyable.cpp
+        : [ requires cxx11_hdr_type_traits ] ]
 
 #   [ compile-fail xxx.cpp  ]
 

test/support/pair_conversion.cpp

@@ -0,0 +1,42 @@
+/*=============================================================================
+    Copyright (c) 2018 Kohei Takahashi
+
+    Distributed under 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)
+==============================================================================*/
+
+#include <utility>
+#include <boost/config.hpp>
+#include <boost/fusion/support/pair.hpp>
+
+using namespace boost::fusion;
+
+struct eat_int
+{
+    eat_int(int);
+};
+
+struct eat_pair
+{
+    template <typename K, typename V>
+    eat_pair(pair<K, V>);
+};
+
+int main()
+{
+    pair<void, int> p;
+
+    pair<void, eat_int> ci(p);
+
+#ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
+    pair<void, eat_int> mi(std::move(p));
+#endif
+
+    // eat_pair can't be converted from int, but can be pair.
+    // So pair(eat_pair) should be called rather than pair(pair<void, eat_pair>).
+    pair<void, eat_pair> cp(p);
+
+#ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
+    pair<void, eat_pair> mp(std::move(p));
+#endif
+}

test/support/pair_nest.cpp

@@ -1,5 +1,5 @@
 /*=============================================================================
-    Copyright (c) 2015 Kohei Takahashi
+    Copyright (c) 2015,2018 Kohei Takahashi
 
     Distributed under 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)
@@ -10,15 +10,20 @@
 using namespace boost::fusion;
 
 template <typename C>
-void copy()
+void copy(C value)
 {
-    pair<int, C> src;
+    pair<int, C> src(value);
     pair<int, C> dest = src;
     boost::ignore_unused(dest);
 }
 
 int main()
 {
-    copy<pair<void, float> >();
+    copy<pair<void, float> >(42.195f);
+    copy<pair<int, float> >(42.195f);
+
+    float f;
+    pair<void, float&> r(f);
+    copy<pair<void, float&> >(r);
 }
 

test/support/pair_trivially_copyable.cpp

@@ -0,0 +1,50 @@
+/*=============================================================================
+    Copyright (c) 2018 Kohei Takahashi
+
+    Distributed under 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)
+==============================================================================*/
+
+#include <type_traits>
+#include <boost/fusion/support/pair.hpp>
+#include <boost/mpl/assert.hpp>
+
+using namespace boost::fusion;
+
+struct non_trivially_copyable
+{
+    non_trivially_copyable(const non_trivially_copyable&);
+    non_trivially_copyable operator=(const non_trivially_copyable&);
+};
+
+struct pod { };
+
+BOOST_MPL_ASSERT_NOT((std::is_trivially_copyable<void>));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<int>));
+BOOST_MPL_ASSERT_NOT((std::is_trivially_copyable<non_trivially_copyable>));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pod>));
+BOOST_MPL_ASSERT_NOT((std::is_trivially_copyable<int&>));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<void*>));
+
+
+
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<void, int> >));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<int, int> >));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<non_trivially_copyable, int> >));
+BOOST_MPL_ASSERT_NOT((std::is_trivially_copyable<pair<int, non_trivially_copyable> >));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<pod, int> >));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<int, pod> >));
+
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<void, int&> >));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<int, int&> >));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<non_trivially_copyable, int&> >));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<int, non_trivially_copyable&> >));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<int, pod&> >));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<int, pod&> >));
+
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<void, int*> >));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<int, int*> >));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<non_trivially_copyable, int*> >));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<int, non_trivially_copyable*> >));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<int, pod*> >));
+BOOST_MPL_ASSERT((std::is_trivially_copyable<pair<int, pod*> >));