[Bug libstdc++/49151] New: [C++0x] chrono::duration has incorrect non-member operator semantics

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49151

           Summary: [C++0x] chrono::duration has incorrect non-member
                    operator semantics
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: daniel.kruegler@googlemail.com


This entry is a reminder for the need to synchronize the library with the
accepted LWG issue 2020,

http://lwg.github.com/issues/lwg-defects.html#2020

The observable behaviour is that the following test code is rejected by gcc
4.7.0 20110521 (experimental) in C++0x mode at the line marked with #:

//----
#include <chrono>

constexpr std::chrono::milliseconds ms{};
constexpr auto res = ms + ms; // #
//----

"error: 'typename std::common_type<std::chrono::duration<_Rep1, _Period1>,
std::chrono::duration<_Rep2, _Period2> >::type std::chrono::operator+(const
std::chrono::duration<_Rep1, _Period1>&, const std::chrono::duration<_Rep2,
_Period2>&) [with _Rep1 = long long int, _Period1 = std::ratio<1ll, 1000ll>,
_Rep2 = long long int, _Period2 = std::ratio<1ll, 1000ll>, typename
std::common_type<std::chrono::duration<_Rep1, _Period1>,
std::chrono::duration<_Rep2, _Period2> >::type = std::chrono::duration<long
long in"