Implement LWG2783: stack::emplace() and queue::emplace() should return decltype(auto)

llvm-svn: 323385

libcxx/include/queue

@@ -290,7 +290,7 @@ public:
     template <class... _Args>
         _LIBCPP_INLINE_VISIBILITY
 #if _LIBCPP_STD_VER > 14
-        reference emplace(_Args&&... __args)
+        decltype(auto) emplace(_Args&&... __args)
             { return c.emplace_back(_VSTD::forward<_Args>(__args)...);}
 #else
         void     emplace(_Args&&... __args)

libcxx/include/stack

@@ -199,7 +199,7 @@ public:
     template <class... _Args>
         _LIBCPP_INLINE_VISIBILITY
 #if _LIBCPP_STD_VER > 14
-        reference emplace(_Args&&... __args)
+        decltype(auto) emplace(_Args&&... __args)
         { return c.emplace_back(_VSTD::forward<_Args>(__args)...);}
 #else
         void      emplace(_Args&&... __args)

libcxx/test/std/containers/container.adaptors/queue/queue.defn/emplace.pass.cpp

@@ -11,19 +11,38 @@
 
 // <queue>
 
-// template <class... Args> reference emplace(Args&&... args);
-// return type is 'reference' in C++17; 'void' before
+// template <class... Args> decltype(auto) emplace(Args&&... args);
+// return type is 'decltype(auto)' in C++17; 'void' before
+//	whatever the return type of the underlying container's emplace_back() returns.
 
 
 #include <queue>
 #include <cassert>
+#include <list>
 
 #include "test_macros.h"
 
 #include "../../../Emplaceable.h"
 
+template <typename Queue>
+void test_return_type() {
+	typedef typename Queue::container_type Container;
+	typedef typename Container::value_type value_type;
+	typedef decltype(std::declval<Queue>().emplace(std::declval<value_type &>()))	  queue_return_type;
+	
+#if TEST_STD_VER > 14
+	typedef decltype(std::declval<Container>().emplace_back(std::declval<value_type>())) container_return_type;
+	static_assert(std::is_same<queue_return_type, container_return_type>::value, "");
+#else
+	static_assert(std::is_same<queue_return_type, void>::value, "");
+#endif
+}
+
 int main()
 {
+	test_return_type<std::queue<int> > ();
+	test_return_type<std::queue<int, std::list<int> > > ();
+	
 	typedef Emplaceable T;
 	std::queue<Emplaceable> q;
 #if TEST_STD_VER > 14

libcxx/test/std/containers/container.adaptors/stack/stack.defn/emplace.pass.cpp

@@ -11,18 +11,37 @@
 
 // <stack>
 
-// template <class... Args> reference emplace(Args&&... args);
-// return type is 'reference' in C++17; 'void' before
+// template <class... Args> decltype(auto) emplace(Args&&... args);
+// return type is 'decltype(auto)' in C++17; 'void' before
+//  whatever the return type of the underlying container's emplace_back() returns.
 
 #include <stack>
 #include <cassert>
+#include <vector>
 
 #include "test_macros.h"
 
 #include "../../../Emplaceable.h"
 
+template <typename Stack>
+void test_return_type() {
+    typedef typename Stack::container_type Container;
+    typedef typename Container::value_type value_type;
+    typedef decltype(std::declval<Stack>().emplace(std::declval<value_type &>()))     stack_return_type;
+    
+#if TEST_STD_VER > 14
+    typedef decltype(std::declval<Container>().emplace_back(std::declval<value_type>())) container_return_type;
+    static_assert(std::is_same<stack_return_type, container_return_type>::value, "");
+#else
+    static_assert(std::is_same<stack_return_type, void>::value, "");
+#endif
+}
+
 int main()
 {
+    test_return_type<std::stack<int> > ();
+    test_return_type<std::stack<int, std::vector<int> > > ();
+
     typedef Emplaceable T;
     std::stack<Emplaceable> q;    
 #if TEST_STD_VER > 14

libcxx/www/cxx2a_status.html

@@ -54,7 +54,7 @@
 <!--
 	<tr><td><a href="https://wg21.link/n3346">3346</a></td><td>LWG</td><td>Terminology for Container Element Requirements - Rev 1</td><td>Kona</td><td>Complete</td><td>3.4</td></tr>
 -->
-	<tr><td><a href="https://wg21.link/P0463R1">P0463R1</a></td><td>LWG</td><td>Endian just Endian</td><td>Toronto</td><td><I>In progress</I></td><td>7.0</td></tr>
+	<tr><td><a href="https://wg21.link/P0463R1">P0463R1</a></td><td>LWG</td><td>Endian just Endian</td><td>Toronto</td><td>Complete</td><td>7.0</td></tr>
 	<tr><td><a href="https://wg21.link/P0674R1">P0674R1</a></td><td>LWG</td><td>Extending make_shared to Support Arrays</td><td>Toronto</td><td></td><td></td></tr>
 
   	<tr><td></td><td></td><td></td><td></td><td></td><td></td></tr>
@@ -94,7 +94,7 @@
 	<tr><td><a href="https://wg21.link/LWG2444">2444</a></td><td>Inconsistent complexity for <tt>std::sort_heap</tt></td><td>Toronto</td><td></td></tr>
 	<tr><td><a href="https://wg21.link/LWG2593">2593</a></td><td>Moved-from state of Allocators</td><td>Toronto</td><td></td></tr>
 	<tr><td><a href="https://wg21.link/LWG2597">2597</a></td><td><tt>std::log</tt> misspecified for complex numbers</td><td>Toronto</td><td></td></tr>
-	<tr><td><a href="https://wg21.link/LWG2783">2783</a></td><td><tt>stack::emplace()</tt> and <tt>queue::emplace()</tt> should return <tt>decltype(auto)</tt></td><td>Toronto</td><td></td></tr>
+	<tr><td><a href="https://wg21.link/LWG2783">2783</a></td><td><tt>stack::emplace()</tt> and <tt>queue::emplace()</tt> should return <tt>decltype(auto)</tt></td><td>Toronto</td><td>Complete</td></tr>
 	<tr><td><a href="https://wg21.link/LWG2932">2932</a></td><td>Constraints on parallel algorithm implementations are underspecified</td><td>Toronto</td><td></td></tr>
 	<tr><td><a href="https://wg21.link/LWG2937">2937</a></td><td>Is <tt>equivalent("existing_thing", "not_existing_thing")</tt> an error</td><td>Toronto</td><td>Complete</td></tr>
 	<tr><td><a href="https://wg21.link/LWG2940">2940</a></td><td><tt>result_of</tt> specification also needs a little cleanup</td><td>Toronto</td><td></td></tr>
@@ -135,7 +135,7 @@
 <!-- 	<tr><td></td><td></td><td></td><td></td></tr> -->
   </table>
 
-  <p>Last Updated: 22-Jan-2018</p>
+  <p>Last Updated: 24-Jan-2018</p>
 </div>
 </body>
 </html>