id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc 11907,Why does BOOST_TEST() treat std::string as a collection?,bspencer@…,Raffi Enficiaud,"Captured from http://lists.boost.org/boost-users/2015/12/85472.php Why does BOOST_TEST() compare std::string values as collections instead of scalars (by default)? It's odd that the following produce different output, for example: {{{ BOOST_TEST(std::string(""a"") == ""b""); BOOST_TEST(std::string(""a"") == std::string(""b"")); }}} This will output: {{{ test.cc(6): error: in ""test"": check std::string(""a"") == ""b"" has failed [a != b] test.cc(7): error: in ""test"": check std::string(""a"") == std::string(""b"") has failed }}} Note the lack of ""[a != b]"" on the second case. Also note that BOOST_CHECK_EQUAL() would emit as in the first form. This seems to be because std::string is_forward_iterable, and thus falls into the collection_comparison_op.hpp comparators instead of the scalar comparators. Is this intentional or an oversight? As a simple fix, adding a condition to the partial specialization of the collection_comparison_op.hpp comparators that specifically excludes std::string is enough to have std::string treated as scalars. For example, to handle std::string but not std::wstring with C++11 support: {{{ template struct name::value && unit_test::is_forward_iterable::value && !(std::is_same::type, std::string>::value || std::is_same::type, std::string>::value) >::type }}} (The above is an example and not a complete change supporting std::wstring and C++98.) The response on the mailing list was that this was a bug, so here's a ticket to help track it :)",Bugs,closed,Boost 1.63.0,test,Boost 1.59.0,Problem,fixed,,