Я пытаюсь сохранить функцию forward в std::function
. Если я использую std::bind
, я получаю сообщение об ошибке, например no viable conversion from ...
. Если я использую лямбду, она скомпилируется.
Вот пример кода
#include <functional>
template<typename Handler>void func1(int a, Handler&& handler) {}
template<typename Handler>void func2(Handler&& handler)
{
// this line compile fine
std::function<void ()> funcA = [handler = std::move(handler)]() { func1(1, std::move(handler)); };
// this line got compile error
std::function<void ()> funcB = std::bind(func1<Handler>, 1, std::move(handler));
}
int main()
{
func2(&main); // this just a sample, I am using functor as argument in real code
}
Попытка как g++ --std = С++ 1y (v4.9.0), так и clang++ --std = С++ 1y (v3.4.1) дает тот же результат
edit: сообщение об ошибке clang++
main.cpp:8:28: error: no viable conversion from 'typename _Bind_helper<__is_socketlike<void (*)(int, int (*&&)())>::value, void (*)(int, int
(*&&)()), int, int (*)()>::type' (aka '_Bind<__func_type (typename decay<int>::type, typename decay<int (*)()>::type)>') to
'std::function<void ()>'
std::function<void ()> funcB = std::bind(&func1<Handler>, 1, std::move(handler));
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
main.cpp:14:5: note: in instantiation of function template specialization 'func2<int (*)()>' requested here
func2(&main);
^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/4.9.0/../../../../include/c++/4.9.0/functional:2181:7: note: candidate constructor not viable: no
known conversion from 'typename _Bind_helper<__is_socketlike<void (*)(int, int (*&&)())>::value, void (*)(int, int (*&&)()), int, int
(*)()>::type' (aka '_Bind<__func_type (typename decay<int>::type, typename decay<int (*)()>::type)>') to 'nullptr_t' for 1st argument
function(nullptr_t) noexcept
^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/4.9.0/../../../../include/c++/4.9.0/functional:2192:7: note: candidate constructor not viable: no
known conversion from 'typename _Bind_helper<__is_socketlike<void (*)(int, int (*&&)())>::value, void (*)(int, int (*&&)()), int, int
(*)()>::type' (aka '_Bind<__func_type (typename decay<int>::type, typename decay<int (*)()>::type)>') to 'const std::function<void ()> &'
for 1st argument
function(const function& __x);
^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/4.9.0/../../../../include/c++/4.9.0/functional:2201:7: note: candidate constructor not viable: no
known conversion from 'typename _Bind_helper<__is_socketlike<void (*)(int, int (*&&)())>::value, void (*)(int, int (*&&)()), int, int
(*)()>::type' (aka '_Bind<__func_type (typename decay<int>::type, typename decay<int (*)()>::type)>') to 'std::function<void ()> &&' for
1st argument
function(function&& __x) : _Function_base()
^
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/4.9.0/../../../../include/c++/4.9.0/functional:2226:2: note: candidate template ignored:
substitution failure [with _Functor = std::_Bind<void (*(int, int (*)()))(int, int (*&&)())>]: no matching function for call to object of
type 'std::_Bind<void (*(int, int (*)()))(int, int (*&&)())>'
function(_Functor);
^
1 error generated.