id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
8452,Conflict between Boost.Format and filtered_graph in Boost.Graph,Jan Hudec <bulb@…>,Samuel Krempp,"I am using `boost::format` in my logging macros and some graphs from
Boost.Graph. But whenever I include `boost/graph/filtered_graph.hpp`, GCC
starts to complain that

{{{
boost/graph/graph_traits.hpp: In instantiation of 'struct boost::graph_traits<char>':
boost/graph/filtered_graph.hpp:131:57:   required from 'struct boost::filtered_graph_base<char>'
boost/graph/filtered_graph.hpp:141:9:   required from 'class boost::filtered_graph<char, std::char_traits<char>, std::allocator<char> >'
boost/format/feed_args.hpp:253:17:   required from 'void boost::io::detail::distribute(boost::basic_format<Ch, Tr, Alloc>&, T) [with Ch = char; Tr = std::char_traits<char>; Alloc = std::allocator<char>; T = const SomeWrapper<lots of boost::graph things here> &]'
boost/format/feed_args.hpp:263:9:   required from 'boost::basic_format<Ch, Tr, Alloc>& boost::io::detail::feed(boost::basic_format<Ch, Tr, Alloc>&, T) [with Ch = char; Tr = std::char_traits<char>; Alloc = std::allocator<char>; T = const SomeWrapper<lots of boost::graph things here> &]'
[... more required froms, don't seem relevant anymore ...]
boost/graph/graph_traits.hpp:33:52: error: 'char' is not a class, struct, or union type
}}}

The `SomeWrapper` is my class for customizing `operator<<`. It's template
argument has few hundred characters. It is pair of iterators into something
complex involving `boost::directed_graph`. The `filtered_graph` is not actually
used, only included.

Both GCC 4.5.2 and 4.7.2 show the above error, but Visual C++ 15.00.30729.01
(Visual Studio 9 2008) compiles it just fine. I am not sure whether it is bug
in GCC or whether MSVC considers SFINAE something that isn't, but it seems to
be the later. The template from `boost/graph/filtered_graph.hpp` will be found
by ADL and because the template parameters are provided explicitly, compiler
must instantiate it to find out whether it is better candidate or not. That
fails, but not in immediate context, so it is not SFINAE.

It can be worked around by qualifying the `put` in `boost/format/feed_args.hpp`,
renaming it, or by modifying the templates in graph_traits and filtered_graph
to make the failure SFINAE (might have some advantages elsewhere).

I had the problem with 1.51 and updated to 1.53, because there are some changes
to `graph_traits` that looked like they may be relevant, but it didn't help.",Bugs,closed,To Be Determined,format,Boost 1.53.0,Problem,invalid,,