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* [Bug c++/52757] New: [C++11] A lamba functions is not able to be used as a function pointer when passed as an explicit template argument @ 2012-03-28 19:59 metaprogrammingtheworld at gmail dot com 2012-03-28 20:10 ` [Bug c++/52757] " redi at gcc dot gnu.org ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: metaprogrammingtheworld at gmail dot com @ 2012-03-28 19:59 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52757 Bug #: 52757 Summary: [C++11] A lamba functions is not able to be used as a function pointer when passed as an explicit template argument Classification: Unclassified Product: gcc Version: 4.7.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ AssignedTo: unassigned@gcc.gnu.org ReportedBy: metaprogrammingtheworld@gmail.com The following are two simple test-cases for what appears to be the same problem. The main issue is that you can't use a lambda function as a template argument where the template parameter type is a function pointer type. It seems that this happens because there is no constexpr conversion operator from the lambda function type to the corresponding function pointer type (in places where the pointer is not required to be a compile-time constant, the conversion works properly, as expected). First test-case: ////////// template< int (*)() > struct foo; typedef foo< [] { return 0; } > bar; ////////// main.cpp:2:31: error: could not convert template argument '{}' to 'int (*)()' main.cpp:2:36: error: invalid type in declaration before ';' token Second test-case (error message may shed light on the root of the problem): ////////// constexpr int (*foo)() = [] { return 0; }; ////////// main.cpp:1:41: error: '<lambda()>::operator int (*)()() const' is not a constexpr function ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/52757] [C++11] A lamba functions is not able to be used as a function pointer when passed as an explicit template argument 2012-03-28 19:59 [Bug c++/52757] New: [C++11] A lamba functions is not able to be used as a function pointer when passed as an explicit template argument metaprogrammingtheworld at gmail dot com @ 2012-03-28 20:10 ` redi at gcc dot gnu.org 2012-03-28 20:13 ` metaprogrammingtheworld at gmail dot com 2012-03-28 20:45 ` redi at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: redi at gcc dot gnu.org @ 2012-03-28 20:10 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52757 --- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-03-28 19:58:41 UTC --- (In reply to comment #0) > that this happens because there is no constexpr conversion operator from the > lambda function type to the corresponding function pointer type Is there supposed to be? "The closure type for a lambda-expression with no lambda-capture has a public non-virtual non-explicit const conversion function to pointer to function having the same parameter and return types as the closure type's function call operator. The value returned by this conversion function shall be the address of a function that, when invoked, has the same effect as invoking the closure type's function call operator." A closure is not literal and its conversion operator isn't constexpr. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/52757] [C++11] A lamba functions is not able to be used as a function pointer when passed as an explicit template argument 2012-03-28 19:59 [Bug c++/52757] New: [C++11] A lamba functions is not able to be used as a function pointer when passed as an explicit template argument metaprogrammingtheworld at gmail dot com 2012-03-28 20:10 ` [Bug c++/52757] " redi at gcc dot gnu.org @ 2012-03-28 20:13 ` metaprogrammingtheworld at gmail dot com 2012-03-28 20:45 ` redi at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: metaprogrammingtheworld at gmail dot com @ 2012-03-28 20:13 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52757 --- Comment #2 from Matt Calabrese <metaprogrammingtheworld at gmail dot com> 2012-03-28 20:10:02 UTC --- Hmm. That seems artificially limiting, but thanks for looking it up -- sorry for the erroneous bug report. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/52757] [C++11] A lamba functions is not able to be used as a function pointer when passed as an explicit template argument 2012-03-28 19:59 [Bug c++/52757] New: [C++11] A lamba functions is not able to be used as a function pointer when passed as an explicit template argument metaprogrammingtheworld at gmail dot com 2012-03-28 20:10 ` [Bug c++/52757] " redi at gcc dot gnu.org 2012-03-28 20:13 ` metaprogrammingtheworld at gmail dot com @ 2012-03-28 20:45 ` redi at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: redi at gcc dot gnu.org @ 2012-03-28 20:45 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52757 Jonathan Wakely <redi at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution| |INVALID --- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-03-28 20:13:37 UTC --- . ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2012-03-28 20:13 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2012-03-28 19:59 [Bug c++/52757] New: [C++11] A lamba functions is not able to be used as a function pointer when passed as an explicit template argument metaprogrammingtheworld at gmail dot com 2012-03-28 20:10 ` [Bug c++/52757] " redi at gcc dot gnu.org 2012-03-28 20:13 ` metaprogrammingtheworld at gmail dot com 2012-03-28 20:45 ` redi at gcc dot gnu.org
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