[Bug libstdc++/56677] New: [ratio] : ratio_multiply, ratio_divide, etc results doesnt verify as __is_ratio

["npl at chello dot at" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56677

             Bug #: 56677
           Summary: [ratio] : ratio_multiply, ratio_divide, etc results
                    doesnt verify as __is_ratio
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: npl@chello.at


within chrono there is a test for template parameters if they classify as
ratios: __is_ratio
this test only works if the type is constructed as ratio<>, but the arithmetic
functions on ratio ratio_multiply, ratio_divide, .. dont generate the result
this way.

Here is a little programm to illustrate the issue:

------------------------------------------------------------------
#include <ratio>
#include <chrono>

typedef std::ratio_divide<std::ratio<1>, std::ratio<1> > ratii1;
typedef std::ratio<ratii1::num,ratii1::den > ratii2;

std::chrono::duration<unsigned long, ratii1 > d1; // compile time check raises
error
std::chrono::duration<unsigned long, ratii2 > d2; // works fine.
------------------------------------------------------------------

the solution would be either to make the  __is_ratio smarter or, just generate
results like I did with ratii2.