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From: "sausage at tehsausage dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/45873] New: Parameter packs not expanding consistently in function return types Date: Sun, 03 Oct 2010 15:55:00 -0000 [thread overview] Message-ID: <bug-45873-4@http.gcc.gnu.org/bugzilla/> (raw) http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45873 Summary: Parameter packs not expanding consistently in function return types Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ AssignedTo: unassigned@gcc.gnu.org ReportedBy: sausage@tehsausage.com Non-variadic templates passed to a function as "template <class ...> class" have inconsistent behavior when provided with a parameter pack as an argument and used as a return type than when used in the body of the function in the same way. I am unsure on the expected behavior or whether passing templates in such a way is even allowed. template <template <class ...> class T, class ...Args> auto foo(Args... args) -> T<Args...> { return T<Args...>(args...); } template <template <class ...> class T, class ...Args> auto bar(Args... args) -> T<int, double> { return T<Args...>(args...); } int main() { foo<pair>(1, 2.0); // error: no matching function for call to 'foo(int, double)' bar<pair>(1, 2.0); // OK, returns pair<int, double> } The following work-around seems to work: template <template <class ...> class T, class ...Args> struct expand { typedef T<Args...> type; }; template <template <class ...> class T, class ...Args> auto baz(Args... args) -> typename expand<T, Args...>::type { return T<Args...>(args...); } int main() { baz(1, 2.0); // OK, returns pair<int, double> }
next reply other threads:[~2010-10-03 15:55 UTC|newest] Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2010-10-03 15:55 sausage at tehsausage dot com [this message] 2010-10-04 8:11 ` [Bug c++/45873] " redi at gcc dot gnu.org 2011-05-16 12:28 ` redi at gcc dot gnu.org 2011-05-16 16:34 ` jason at gcc dot gnu.org 2011-05-16 17:40 ` redi at gcc dot gnu.org 2012-04-16 2:11 ` [Bug c++/45873] [C++0x] " jason at gcc dot gnu.org
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