Re: [boost] [Range] begin/end ADL issues in C++0x range-based for

Subject: Re: [boost] [Range] begin/end ADL issues in C++0x range-based for
From: Dave Abrahams (dave_at_[hidden])
Date: 2010-12-17 19:23:17

At Sat, 18 Dec 2010 07:20:56 +0900,
Michel MORIN wrote:
> 
> #ifndef BOOST_NO_RANGE_BASED_FOR
> namespace boost {
>     using std::begin;
> 
>     // has_begin metafunction...
> 
>     template <typename Range>
>     inline typename boost::range_iterator<Range>::type
>     begin(Range& rng, typename
> disable_if<range_detail::has_begin<Range>>::type* = 0)
>     {
>         return range_begin(rng);
>     }
> 	
> 	// const version ...
> }
> #else
> // existing code...
> 
> For details, see the attached.
> I also attach a patch for Boost.Config to add BOOST_NO_RANGE_BASED_FOR.
> Any comments or thoughs?

First, Michel, thanks for addressing this important matter.  2nd, I'm
a wee bit worried about ODR issues.  At first it looks like you're
saying to define has_begin in namespace boost.  Then your code seems
to imply it's in namespace range_detail.  I think the latter is
probably OK, but not the former.  The key thing is that the definition
of boost::begin should not itself alter the result of has_begin for
any given type.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com