From 50fe0c7d61131dd693fce234573e30441eb35b38 Mon Sep 17 00:00:00 2001
From: Marshall Clow <mclow.lists@gmail.com>
Date: Mon, 3 Mar 2014 06:18:11 +0000
Subject: [PATCH] Implement LWG Paper n3887: Consistent Metafunction Aliases.
 This adds std::tuple_element_t<> as an alias for tuple_element<>::type. Clean
 up the synopsis for tuple_element in <utility> as well.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@202673 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/tuple                                 |  9 ++++++-
 include/utility                               | 24 +++++++++----------
 .../tuple.helper/tuple_element.pass.cpp       |  7 ++++++
 www/cxx1y_status.html                         |  2 +-
 4 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/include/tuple b/include/tuple
index 30a958abc..3a1752ee1 100644
--- a/include/tuple
+++ b/include/tuple
@@ -82,13 +82,15 @@ template <class T> class tuple_size; // undefined
 template <class... T> class tuple_size<tuple<T...>>;
 template <intsize_t I, class T> class tuple_element; // undefined
 template <intsize_t I, class... T> class tuple_element<I, tuple<T...>>;
+template <size_t _Ip, class ..._Tp>
+  using tuple_element_t = typename tuple_element <_Ip, _Tp...>::type; // C++14
 
 // 20.4.1.5, element access:
 template <intsize_t I, class... T>
     typename tuple_element<I, tuple<T...>>::type&
     get(tuple<T...>&) noexcept; // constexpr in C++14
 template <intsize_t I, class... T>
-    typename tuple_element<I, tuple<T...>>::type const&
+    typename const tuple_element<I, tuple<T...>>::type &
     get(const tuple<T...>&) noexcept; // constexpr in C++14
 template <intsize_t I, class... T>
     typename tuple_element<I, tuple<T...>>::type&&
@@ -152,6 +154,11 @@ public:
     typedef typename tuple_element<_Ip, __tuple_types<_Tp...> >::type type;
 };
 
+#if _LIBCPP_STD_VER > 11
+template <size_t _Ip, class ..._Tp>
+using tuple_element_t = typename tuple_element <_Ip, _Tp...>::type;
+#endif
+
 // __tuple_leaf
 
 template <size_t _Ip, class _Hp, bool=is_empty<_Hp>::value
diff --git a/include/utility b/include/utility
index 0a1a7f1d9..8a7e1dcb9 100644
--- a/include/utility
+++ b/include/utility
@@ -101,30 +101,30 @@ constexpr piecewise_construct_t piecewise_construct = piecewise_construct_t();
 template <class T> class tuple_size;
 template <size_t I, class T> class tuple_element;
 
-template <class T1, class T2> struct tuple_size<std::pair<T1, T2> >;
-template <class T1, class T2> struct tuple_element<0, std::pair<T1, T2> >;
-template <class T1, class T2> struct tuple_element<1, std::pair<T1, T2> >;
+template <class T1, class T2> struct tuple_size<pair<T1, T2> >;
+template <class T1, class T2> struct tuple_element<0, pair<T1, T2> >;
+template <class T1, class T2> struct tuple_element<1, pair<T1, T2> >;
 
 template<size_t I, class T1, class T2>
-    typename tuple_element<I, std::pair<T1, T2> >::type&
-    get(std::pair<T1, T2>&) noexcept; // constexpr in C++14
+    typename tuple_element<I, pair<T1, T2> >::type&
+    get(pair<T1, T2>&) noexcept; // constexpr in C++14
 
 template<size_t I, class T1, class T2>
-    const typename const tuple_element<I, std::pair<T1, T2> >::type&
-    get(const std::pair<T1, T2>&) noexcept; // constexpr in C++14
+    const typename const tuple_element<I, pair<T1, T2> >::type&
+    get(const pair<T1, T2>&) noexcept; // constexpr in C++14
 
 template<size_t I, class T1, class T2>
-    typename tuple_element<I, std::pair<T1, T2> >::type&&
-    get(std::pair<T1, T2>&&) noexcept; // constexpr in C++14
+    typename tuple_element<I, pair<T1, T2> >::type&&
+    get(pair<T1, T2>&&) noexcept; // constexpr in C++14
 
 template<class T1, class T2>
-    constexpr T1& get(std::pair<T1, T2>&) noexcept; // C++14
+    constexpr T1& get(pair<T1, T2>&) noexcept; // C++14
 
 template<size_t I, class T1, class T2>
-    constexpr T1 const& get(std::pair<T1, T2> const &) noexcept; // C++14
+    constexpr T1 const& get(pair<T1, T2> const &) noexcept; // C++14
 
 template<size_t I, class T1, class T2>
-    constexpr T1&& get(std::pair<T1, T2>&&) noexcept; // C++14
+    constexpr T1&& get(pair<T1, T2>&&) noexcept; // C++14
 
 // C++14
 
diff --git a/test/utilities/tuple/tuple.tuple/tuple.helper/tuple_element.pass.cpp b/test/utilities/tuple/tuple.tuple/tuple.helper/tuple_element.pass.cpp
index 7b1ff8bb1..f3f8f2b10 100644
--- a/test/utilities/tuple/tuple.tuple/tuple.helper/tuple_element.pass.cpp
+++ b/test/utilities/tuple/tuple.tuple/tuple.helper/tuple_element.pass.cpp
@@ -28,7 +28,14 @@ void test()
     static_assert((std::is_same<typename std::tuple_element<N, const T>::type, const U>::value), "");
     static_assert((std::is_same<typename std::tuple_element<N, volatile T>::type, volatile U>::value), "");
     static_assert((std::is_same<typename std::tuple_element<N, const volatile T>::type, const volatile U>::value), "");
+#if _LIBCPP_STD_VER > 11
+    static_assert((std::is_same<typename std::tuple_element_t<N, T>, U>::value), "");
+    static_assert((std::is_same<typename std::tuple_element_t<N, const T>, const U>::value), "");
+    static_assert((std::is_same<typename std::tuple_element_t<N, volatile T>, volatile U>::value), "");
+    static_assert((std::is_same<typename std::tuple_element_t<N, const volatile T>, const volatile U>::value), "");
+#endif
 }
+
 int main()
 {
     test<std::tuple<int>, 0, int>();
diff --git a/www/cxx1y_status.html b/www/cxx1y_status.html
index c698463a8..d1632c50a 100644
--- a/www/cxx1y_status.html
+++ b/www/cxx1y_status.html
@@ -100,7 +100,7 @@
  	<tr><td></td><td></td><td></td><td></td><td></td><td></td></tr>
 
 	<tr><td><a href="http://wiki.edg.com/twiki/pub/Wg21issaquah/FormalMotions/N3924_rand-note-v2.pdf">3924</a></td><td>LWG</td><td>Discouraging rand() in C++14</td><td>Issaquah</td><td></td><td></td></tr>
-	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3887">3887</a></td><td>LWG</td><td>Consistent Metafunction Aliases</td><td>Issaquah</td><td></td><td></td></tr>
+	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3887">3887</a></td><td>LWG</td><td>Consistent Metafunction Aliases</td><td>Issaquah</td><td></td><td>Complete</td></tr>
 
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