c++ - Given the following, what type is "function"? -

given following, type "function"?

#include <functional> #include <vector>  template<class t> class foo { public:      template<typename p, typename q, typename r, typename... args>     void attach(p (q::*f)(args...), r p)     {         auto function = [p, f](args... args)         {             (*p.*f)(args...);         };          listeners.push_back(function);     }     private:      std::vector<std::function<t>> listeners; };  class bar { public:      int handler(int x, int y, int z)     {         return 0;     } };  int main(void) {     auto foo = foo<int(int, int, int)>();     auto bar = bar();      foo.attach(&bar::handler, &bar); } 

for context i'm attempting make lambda calls method on instance, storing lambda collection. push_back fails compile, following error:

xrefwrap(283): error c2440: 'return' : cannot convert 'void' 'int'

i using std::bind make std::function store. apparently may able lambda (and variadic templates, don't need 1 template per arity) far it's defeating me.

when have constructed foo, explicit template argument supplied auto foo = foo<int(int, int, int)>();,

int main(void) {     auto foo = foo<int(int, int, int)>(); //<<<< here template arguments when constructing foo      auto bar = bar();      foo.attach(&bar::handler, &bar); } 

where when registering listener function signatures return type void

auto function = [p, f](args... args)     {         (*p.*f)(args...);     }; 

resolution

so either

• change explicit template argument of foo, auto foo = foo<void(int, int, int)>(); return void match listener callback.
• or ensure listener function returns integer. return (*p.*f)(args...);

note may intended return status code listener might have missed? second resolution point looks me obvious plausible issue