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From: "w.shane.grant at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/56774] New: G++ 4.8 reverses variadic template types during unpacking Date: Thu, 28 Mar 2013 21:22:00 -0000 [thread overview] Message-ID: <bug-56774-4@http.gcc.gnu.org/bugzilla/> (raw) http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56774 Bug #: 56774 Summary: G++ 4.8 reverses variadic template types during unpacking Classification: Unclassified Product: gcc Version: 4.8.0 Status: UNCONFIRMED Severity: major Priority: P3 Component: c++ AssignedTo: unassigned@gcc.gnu.org ReportedBy: w.shane.grant@gmail.com In g++ 4.8, it seems as if variadic templates are reversed when being unpacked. Consider the following minimal example: #include <tuple> #include <iostream> template <class T, class ... OtherT> void something( std::tuple<T, OtherT...> & tup ) { std::cout << std::get<1>(tup) << std::endl; } int main() { std::tuple<int, char, bool> myTuple(3, 'a', true); // Compiles OK in GCC 4.6.3 but NOT 4.8 something<int, char, bool>( myTuple ); // Compiles OK in GCC 4.8 but NOT 4.6.3 something<int, bool, char>( myTuple ); return 0; } The output of this, if the appropriate line is commented out, will be: 'a'. To get code that previously worked under 4.6.3, the template parameters that will be unpacked have to be reversed. See relevant Stack Overflow post here: http://stackoverflow.com/questions/15692112/gcc-4-8-is-reversing-variadic-template-parameter-pack
next reply other threads:[~2013-03-28 21:22 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-03-28 21:22 w.shane.grant at gmail dot com [this message] 2013-03-28 23:57 ` [Bug c++/56774] [4.7/4.8/4.9 Regression] " paolo.carlini at oracle dot com 2013-03-29 0:09 ` d.frey at gmx dot de 2013-03-29 0:17 ` paolo.carlini at oracle dot com 2013-03-29 0:21 ` w.shane.grant at gmail dot com 2013-03-29 18:33 ` jason at gcc dot gnu.org 2013-03-30 0:31 ` jason at gcc dot gnu.org
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