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

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

[npl at chello dot at]

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.

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

[redi at gcc dot gnu.org]

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

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-03-21 13:17:15 UTC ---
This is because ratio_divide is a struct, as required by earlier C++0x drafts,
not an alias template as required by the final standard. It's already fixed for
4.8

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

[redi at gcc dot gnu.org]

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

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
      Known to work|                            |4.8.0

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-03-21 13:44:21 UTC ---
The workaround is simply:

std::chrono::duration<unsigned long, ratii1::type > d1;

I don't think we want to backport the fix, as it would break compatibility with
existing 4.7.x releases.

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

[npl at chello dot at]

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

--- Comment #3 from npl at chello dot at 2013-03-21 14:38:48 UTC ---
Thanks, this did not occur to me.
Still, wouldnt it be relatively easy to adopt the __is_ratio function to check
for the ::type instead?

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

[redi at gcc dot gnu.org]

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

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-03-21 15:35:46 UTC ---
That wouldn't help. The requirement is that the Period template argument is a
ratio. In GCC 4.7 ratio_divide is not a ratio.  Whether ratio_divide::type is a
ratio or not doesn't change the fact that ratio_divide is not a ratio and
therefore not a suitable template argument for duration.

To make it work we'd also need to make duration::period a typedef for either
_Period or _Period::type and alter the two static assertions to use period not
_Period, which is doable but I'm not convinced it's worth fixing in the stable
release branch.  I might look into it later.

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

[paolo.carlini at oracle dot com]

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

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |FIXED

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Fixed for 4.8.0.