http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49251
Summary: [C++0x][parameter pack expanding] unused parameter warning with unpacking empty tuples Product: gcc Version: 4.6.0 Status: UNCONFIRMED Severity: trivial Priority: P3 Component: c++ AssignedTo: unassig...@gcc.gnu.org ReportedBy: gintensub...@gmail.com #include <tuple> template< std::size_t... Indices > struct indices {}; template< class... Args > void sink( Args&&... ) {} template< class Tuple, std::size_t... Indices > void unpack_test( Tuple && t, indices<Indices...> ) { sink( std::get<Indices>(t)... ); } int main() { unpack_test( std::tuple<>(), indices<>() ); } ------------------------ This code, which is unpacking tuples, raises unused parameter warning: $ g++ -std=c++0x -Wunused-parameter bug.cc bug.cc: In instantiation of 'void unpack_test(Tuple&&, indices<Indices ...>) [with Tuple = std::tuple<>, unsigned int ...Indices = {}]': bug.cc:15:44: instantiated from here bug.cc:10:6: warning: unused parameter 't' [-Wunused-parameter] I've confirmed this behavior on following versions: 4.5.0 4.5.3 4.6.0 4.6-20110527 4.7-20110528 It can be avoided by using the parameter explicitly, like `(void)t;', but it's not always used. ( For example, it cannot be used for constexpr functions. )