[Bug libstdc++/77528] std::queue default constructor unnecessarily creates temporary of underlying Container

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77528

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2016-09-08
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Untested fix:

--- a/libstdc++-v3/include/bits/stl_queue.h
+++ b/libstdc++-v3/include/bits/stl_queue.h
@@ -143,12 +143,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       queue(const _Sequence& __c = _Sequence())
       : c(__c) { }
 #else
+      template<typename _Seq = _Sequence, typename _Requires =
+              typename enable_if<is_default_constructible<_Seq>::value>::type>
+       queue()
+       : c() { }
+
       explicit
       queue(const _Sequence& __c)
       : c(__c) { }

       explicit
-      queue(_Sequence&& __c = _Sequence())
+      queue(_Sequence&& __c)
       : c(std::move(__c)) { }

       template<typename _Alloc, typename _Requires = _Uses<_Alloc>>