[boost] Re: [multi_index + mpl + bind] Regression?

From: David Abrahams (dave_at_[hidden])
Date: 2004-09-27 08:52:43

Vladimir Prus <ghost_at_[hidden]> writes:

> David Abrahams wrote:
>
>>> Well, I can tell one third of the story. The reverse_iter_fold.hpp has
>>> this:
>>>
>>>    namespace boost { namespace mpl {
>>>  
>>>     template<
>>>           typename BOOST_MPL_AUX_NA_PARAM(Sequence)
>>>          , typename BOOST_MPL_AUX_NA_PARAM(State)
>>>          , typename BOOST_MPL_AUX_NA_PARAM(BackwardOp)
>>>          , typename ForwardOp = arg<1>
>>>
>>> According to the error message, gcc associates 'arg<1>' with boost::arg
>>> (from bind/arg.hpp), while most likely mpl::arg<1> was meant. Two
>>> remaining questions are
>>> - why gcc does that.
>> 
>> GCC applies "ADL" to almost everything.  It's ridiculous.
>
> Do you know if there is bug report about this? I could not find any in gcc's
> bugzilla. Besides, I'm not sure gcc is at fault. Here's a completely
> distilled testcase:
>
>    namespace boost
>    {  
>        template<int I> class arg {};
>    }
>
>    namespace mpl_ 
>    {
>        template< int N > struct arg {};
>    }
>
>     namespace boost { namespace mpl {
>
>         using namespace mpl_;
>
>         template<typename ForwardOp = arg<1> >
>         struct XXX
>         {
>
> IIRC, the 'arg' visible via using is considered to be declared in the
> nearest namespace enclosing both mpl_ and boost::mpl -- which is global
> namespace. So boost::arg hides mpl_::arg. For explicit mpl::aux, the name
> lookup ignores the 'boost' namespace.

But the fact that explicit qualification doesn't fix it is surely a
bug?

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com