Re: [Boost-users] [variant][graph] Conflict ?

Subject: Re: [Boost-users] [variant][graph] Conflict ?
From: Jeremiah Willcock (jewillco_at_[hidden])
Date: 2010-01-14 11:45:41

On Thu, 14 Jan 2010, Maxime van Noppen wrote:

> Hi,
>
> I recently upgraded the boost version used four our project from boost
> 1.39 to boost 1.41 and encountered a very strange compilation error. I
> managed to reduce the problem to this minimal test case :
>
> ----------var.cc---------------
> #include <boost/variant.hpp>
> #include <boost/graph/breadth_first_search.hpp>
>
> int main()
> {
>  boost::variant<char, bool> v;
>
>  boost::get<int>(v);
> }
> ----------------------------
>
> This doesn't compile on Linux 64bits with gcc 4.4.2 20091208 and
> produces this error message :
>
> ----------------------------
>> In file included from /usr/include/boost/graph/graph_concepts.hpp:17,
>>                  from /usr/include/boost/graph/breadth_first_search.hpp:21,
>>                  from var.cc:2:
>> /usr/include/boost/property_map/property_map.hpp: In instantiation of ‘boost::property_traits<int>’:
>> /usr/include/boost/graph/two_bit_color_map.hpp:46:   instantiated from ‘boost::two_bit_color_map<int>’
>> var.cc:8:   instantiated from here
>> /usr/include/boost/property_map/property_map.hpp:31: error: ‘int’ is not a class, struct, or union type
>> /usr/include/boost/property_map/property_map.hpp:32: error: ‘int’ is not a class, struct, or union type
>> /usr/include/boost/property_map/property_map.hpp:33: error: ‘int’ is not a class, struct, or union type
>> /usr/include/boost/property_map/property_map.hpp:34: error: ‘int’ is not a class, struct, or union type
> ----------------------------
>
> Could there be a conflict between boost.variant and boost.graph or did I
> miss something ?

Yes, there is a conflict like you said.  Both libraries define boost::get, 
and Variant's non-deducible template parameter makes the normal overload 
resolution mechanisms in C++ fail.  I do not have a good workaround for 
that; BGL's get might be safe to have in a nested namespace since it's not 
supposed to be called qualified AFAIK, but people are likely to be calling 
it that way.

-- Jeremiah Willcock