boost::get() calls wrongly resolved by g++

[Roland Levillain <roland@…>]

Boost 1.49.0 seems to make g++ wrongly resolve some calls to boost::get().

The attached C++ code boost-get-test-ko.cc does not compile properly with all the g++ compiler I used (Apple g++ 4.2, ​MacPorts g++ 4.4, 4.5, 4.6, 4.7) on my machine (2010 MacBook Pro w/ Mac OS X version 10.6.8 and Boost 1.49.0 from the MacPorts). These compilers try to use boost::get() from boost/graph/reverse_graph.hpp instead of boost::get() from boost/variant/get.hpp, leading to this kind of error messages:

% g++-mp-4.7 -I/opt/local/include boost-get-test-ko.cc
In file included from /opt/local/include/boost/graph/vector_as_graph.hpp:23:0,
                 from /opt/local/include/boost/graph/transitive_closure.hpp:17,
                 from boost-get-test-ko.cc:2:
/opt/local/include/boost/graph/graph_traits.hpp: In instantiation of 'struct boost::graph_traits<int>':
/opt/local/include/boost/graph/reverse_graph.hpp:472:1:   required by substitution of 'template<class Graph, class GRef> typename boost::graph_traits<Graph>::edge_descriptor boost::get(boost::edge_underlying_t, const boost::reverse_graph<BidirectionalGraph, GraphRef>&, const typename boost::graph_traits<boost::reverse_graph<BidirectionalGraph, GraphRef> >::edge_descriptor&) [with Graph = int; GRef = <missing>]'
boost-get-test-ko.cc:7:28:   required from here
/opt/local/include/boost/graph/graph_traits.hpp:30:52: error: 'int' is not a class, struct, or union type
/opt/local/include/boost/graph/graph_traits.hpp:31:52: error: 'int' is not a class, struct, or union type
/opt/local/include/boost/graph/graph_traits.hpp:32:52: error: 'int' is not a class, struct, or union type
/opt/local/include/boost/graph/graph_traits.hpp:33:52: error: 'int' is not a class, struct, or union type
/opt/local/include/boost/graph/graph_traits.hpp:34:52: error: 'int' is not a class, struct, or union type
/opt/local/include/boost/graph/graph_traits.hpp:35:52: error: 'int' is not a class, struct, or union type
/opt/local/include/boost/graph/graph_traits.hpp:36:52: error: 'int' is not a class, struct, or union type
/opt/local/include/boost/graph/graph_traits.hpp:38:52: error: 'int' is not a class, struct, or union type
/opt/local/include/boost/graph/graph_traits.hpp:39:52: error: 'int' is not a class, struct, or union type
/opt/local/include/boost/graph/graph_traits.hpp:40:52: error: 'int' is not a class, struct, or union type
/opt/local/include/boost/graph/graph_traits.hpp:42:52: error: 'int' is not a class, struct, or union type
/opt/local/include/boost/graph/graph_traits.hpp:43:52: error: 'int' is not a class, struct, or union type
/opt/local/include/boost/graph/graph_traits.hpp:44:52: error: 'int' is not a class, struct, or union type

If the #include <boost/graph/transitive_closure.hpp> statement is removed (see attached file boost-get-test-ok.cc, no compiling error arises.

This problem looks very similar to ticket #4838.

I have obtained similar results with SVN Boost on this platform as well as on Debian GNU/Linux 6.0.4 on x86-64 with g++ 4.4.

The versions of clang++ I tried (MacPorts clang++ 2.9, 3.0 and 3.1 on Mac OS X version 10.6 and clang 3.0 on Debian GNU/Linux 6.0.4) have no trouble compiling both files.

[Jeremiah Willcock]

(In [78315]) Edited reverse_graph to fix test case; fixes #6858

[Jeremiah Willcock]

I've changed reverse_graph to use enable_if to work around this problem; that might break compilers with weak SFINAE support, however.

[Roland Levillain <roland@…>]

Replying to jewillco:

I've changed reverse_graph to use enable_if to work around this problem; that might break compilers with weak SFINAE support, however.

Thanks!