http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51829
Bug #: 51829
Summary: decltype() deduces non-const but only in a template
Classification: Unclassified
Product: gcc
Version: 4.6.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: [email protected]
ReportedBy: [email protected]
The problem rejects a valid `auto expr = ...;` initialization. I have reduced
things to the following (full preprocessed version attached)
The template arguments aren't relevant (unused).
#include <boost/spirit/include/qi_eps.hpp>
template <typename> // without template, works!
void bug()
{
const auto& e1 = boost::spirit::qi::eps(false);
const auto& e2 = e1 | '1';
decltype(boost::spirit::qi::eps(false) | '1') *notok;
notok = &e2; // FAILS if in template function
}
int main() { bug<void>(); }
By using a pointer declaration for `notok` I was able to use demangling to
print the difference between the deduced types:
boost::proto::exprns_::expr<boost::proto::tagns_::tag::bitwise_or,
boost::proto::argsns_::list2<boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal,
boost::proto::argsns_::term<boost::spirit::terminal_ex<boost::spirit::tag::eps,
boost::fusion::vector1<bool> > >, 0l> const&,
boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal,
boost::proto::argsns_::term<char const&>, 0l> >, 2l>
boost::proto::exprns_::expr<boost::proto::tagns_::tag::bitwise_or,
boost::proto::argsns_::list2<boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal,
boost::proto::argsns_::term<boost::spirit::terminal_ex<boost::spirit::tag::eps,
boost::fusion::vector1<bool> > >, 0l> CONST&,
boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal,
boost::proto::argsns_::term<char const&>, 0l> >, 2l> const*
The 'CONST' I capitalized in the middle, is missing when the decltype() is in a
function template, which prevents the assignment.
I don't know how to further reduce the testcase at this point in time. MSVC
2010 compiles the code without problem.
