Hi! This is a follow up to: http://article.gmane.org/gmane.comp.lib.boost.devel/165366 I have been using it since then, but I recently hit a problem when more than one namespace are associated to a type. Example: #include <boost/utility/swap.hpp> #define BOOST_INCLUDE_MAIN #include <boost/test/test_tools.hpp> #include <boost/array.hpp> int test_main( int , char*[] ) { // boost::array or anything in boost such that pair_type has std and // boost as associated namespaces typedef ::std::pair< ::boost::array< int , 1 > , int > pair_type ; pair_type p1 ; pair_type p2 ; p1.first[ 0 ] = p1.second = 0 ; p2.first[ 0 ] = p2.second = 1 ; ::boost::swap( p1 , p2 ) ; // whatever here, it doesn't matter BOOST_CHECK_EQUAL( p2.first[ 0 ] , 0 ) ; BOOST_CHECK_EQUAL( p2.second , 0 ) ; BOOST_CHECK_EQUAL( p1.first[ 0 ] , 1 ) ; BOOST_CHECK_EQUAL( p1.second , 1 ) ; return 0 ; } //----------------------------------------------------------------- Compiling this results in an ambiguity in the call of overloaded swap (at least, with gcc-4.0.2 and gcc-4.2.0): ../../../../boost/utility/swap.hpp: In function 'void boost_swap_impl::swap_impl(T&, T&) [with T = std::pair<boost::array<int, 1ul>, int>]': ../../../../boost/utility/swap.hpp:31: instantiated from 'void boost::swap_adl_barrier::swap(T&, T&) [with T = test_main(int, char**)::pair_type]' std_and_boost.cpp:17: instantiated from here ../../../../boost/utility/swap.hpp:20: error: call of overloaded 'swap(std::pair<boost::array<int, 1ul>, int>&, std::pair<boost::array<int, 1ul>, int>&)' is ambiguous /usr/lib/gcc/x86_64-redhat-linux/4.0.2/../../../../include/c++/4.0.2/bits/stl_algobase.h:92: note: candidates are: void std::swap(_Tp&, _Tp&) [with _Tp = std::pair<boost::array<int, 1ul>, int>] ../../../../boost/utility/swap.hpp:29: note: void boost::swap_adl_barrier::swap(T&, T&) [with T = test_main(int, char**)::pair_type] I tried to move boost::swap_adl_barrier::swap to boost_swap_adl_barrier::swap, but I still got the same error. I find it strange because I thought that 'using' directives were ignored for ADL. I also tried to write in namespace boost "using namespace boost_swap_adl_barrier;", but then the compiler complains that boost::swap is not found. So, is it a compiler bug, an ADL limitation, or is there a solution? For reference, here is the content of boost/utility/swap.hpp (stripped down a little): // Copyright (C) 2007 Steven Watanabe, Joseph Gauterin #include <algorithm> //for std::swap namespace boost_swap_impl { template<class T> void swap_impl(T& left, T& right) { using std::swap;//use std::swap if argument dependent lookup fails swap(left,right); } } namespace boost { namespace swap_adl_barrier { template<class T> void swap(T& left, T& right) { ::boost_swap_impl::swap_impl(left, right); } } using swap_adl_barrier::swap; } -- Francois Duranleau