c++ - moving std::function into another std::function does not invoke move constructor on captured variables -

i have class a prints out message when constructed/copied/moved

class { public:     a(std::string s)         :s_(s)     {         std::cout << "a constructed\n";     }     ~a()     {         std::cout << "a destructed\n";     }     a(const a& a)         :s_(a.s_)     {         std::cout << "a copy constructed\n";     }     a(a&& a)        :s_(std::move(a.s_))     {         std::cout << "a moved\n";     }      std::string s_; }; 

in main, construct instance of a, capture in lambda value, copy lambda std::function, , move std::function std::function

int main() {     a("hello ");     std::function<void()> f = [a]{ std::cout << a.s_; };     std::function<void()> g(std::move(f)); } 

this prints out following

a constructed copy constructed copy constructed destructed destructed destructed 

why move constructor of a not invoked? shouldn't last step of moving f g have invoked a's move constructor?

the copy constructor isn't called precisely because have moved std::function. because std::function can optionally store captured values on heap , retain pointer them. moving function requires moving internal pointer. msvc opts store captures on heap , gcc etc. opt store them on stack requiring captured values moved well.

edit: mooing duck pointing out in comment on question gcc storing captures on heap. actual difference seems gcc moves captures lambda std::function when constructed lambda.