Ich spiele mit Tupeln als Kompilierzeitlisten. In How can I have multiple parameter packs in a variadic template? habe ich mich mit Code geantwortet, der sowohl in GCC als auch in Clang funktioniert, aber Clang wird jetzt nicht kompilieren, dass ich (was ich denke) perfekte Weiterleitung hinzugefügt habe. Es beschwert sich, dass As...
und as...
verschiedene Längen in std::forward<As>(as)...
haben. Wie kann das sein, wenn As...
der Typ as...
ist? Es ist As&&... as
in den Parametern.Ist das ein Compiler Bug oder ein Programmer Bug?
#include <iostream>
#include <tuple>
template < typename ... >
struct two_impl {};
// Base case
template < typename F,
typename ...Bs >
struct two_impl < F, std::tuple <>, std::tuple<Bs...> > {
void operator()(F&& f, Bs&&... bs) {
f(std::forward<Bs>(bs)...);
}
};
// Recursive case
template < typename F,
typename A,
typename ...As,
typename ...Bs >
struct two_impl < F, std::tuple< A, As... >, std::tuple< Bs...> > {
void operator()(F&& f, A&& a, As&&... as, Bs&&... bs) {
auto impl = two_impl < F, std::tuple < As&&... >, std::tuple < Bs&&..., A&& > >();
impl(std::forward<F>(f), std::forward<As>(as)..., std::forward<Bs>(bs)..., std::forward<A>(a));
}
};
template < typename F, typename ...Ts >
void two(F&& f, Ts&& ...ts) {
auto impl = two_impl< F, std::tuple <Ts...>, std::tuple <> >();
impl(std::forward<F>(f), std::forward<Ts>(ts)...);
}
struct Test {
void operator()(int i, float f, double d) {
std::cout << i << std::endl << f << std::endl << d << std::endl;
}
};
int main() {
two(Test(), 1, 1.5f, 2.1);
}
Kompilieren mit clang -lstdc++ -std=c++0x multiple_parameter_packs.cpp
clang -lstdc++ -std=c++0x multiple_parameter_packs.cpp
multiple_parameter_packs.cpp:24:50: error: pack expansion contains parameter packs 'As' and 'as' that have different
lengths (1 vs. 2)
impl(std::forward<F>(f), std::forward<As>(as)..., std::forward<Bs>(bs)..., std::forward<A>(a));
~~ ~~^
multiple_parameter_packs.cpp:24:5: note: in instantiation of member function 'two_impl<Test, std::tuple<float &&,
double &&>, std::tuple<int &&> >::operator()' requested here
impl(std::forward<F>(f), std::forward<As>(as)..., std::forward<Bs>(bs)..., std::forward<A>(a));
^
multiple_parameter_packs.cpp:31:3: note: in instantiation of member function 'two_impl<Test, std::tuple<int, float,
double>, std::tuple<> >::operator()' requested here
impl(std::forward<F>(f), std::forward<Ts>(ts)...);
^
multiple_parameter_packs.cpp:41:3: note: in instantiation of function template specialization
'two<Test, int, float, double>' requested here
two(Test(), 1, 1.5f, 2.1);
^
1 error generated.
Compilation exited abnormally with code 1 at Fri Mar 23 14:25:14
Reduzierte Testfall: http://ideone.com/YA6ao – kennytm
Der Compiler nicht Ihre Bs –