Re: [boost] [type_traits] Big changes in develop

Subject: Re: [boost] [type_traits] Big changes in develop
From: Peter Dimov (lists_at_[hidden])
Date: 2015-05-27 09:12:40

John Maddock wrote:
> On 27/05/2015 07:11, Vicente J. Botet Escriba wrote:
> > We will need a patch that works for the versions of SunPro providing 
> > __typeof__. But shouldn't this be part of Boost.Typeof? Could you 
> > provide such a patch?
>
> Yes Boost.Typeof needs patching as well, ...

Boost.Typeof already appears to use __typeof__:

#elif defined(__SUNPRO_CC)
#   if (__SUNPRO_CC < 0x590 )
#     ifdef BOOST_TYPEOF_NATIVE
#         error native typeof is not supported
#     endif
#     ifndef BOOST_TYPEOF_EMULATION
#         define BOOST_TYPEOF_EMULATION
#     endif
#   else
#     ifndef BOOST_TYPEOF_EMULATION
#         ifndef BOOST_TYPEOF_NATIVE
#             define BOOST_TYPEOF_NATIVE
#         endif
#         define BOOST_TYPEOF_KEYWORD __typeof__
#     endif
#   endif

> ... but note that since one goal of the rewrite is to reduce the libraries 
> dependencies, Boost.Typeof is used as a last resort in common_type, and 
> typeof is used directly when available.

Do we have to use Typeof in common_type at all? In the cases in which 
common_type<T, U>::type is either T or U, can we not find that out by using 
two overloads? Is this not good enough?