c++ - Why does std::is_function evaluate to false when using on a dereferenced function pointer? -

i trying use std::is_function determine if variable function pointer.

when running following code

#include <iostream> #include <typeinfo>  using namespace std;  int main() {     typedef int(*functionpointer)();      functionpointer pmain = main;      cout << typeid(functionpointer).name() << " "<< is_function<functionpointer>::value << endl;     cout << typeid(decltype(pmain)).name() << " " << is_function<decltype(pmain)>::value << endl;      cout << typeid(decltype(main)).name() << " " << is_function<decltype(main)>::value << endl;     cout << typeid(decltype(*pmain)).name() << " " << is_function<decltype(*pmain)>::value << endl;      return 0; } 

the output is

pfive 0 pfive 0 5 1 5 0 

can insight explain why last expression of std::is_function evaluates false?

(code tested under g++4.7, g++4.8 , clang++3.2)

that because decltype(*pmain) yield reference function type, std::function false intended. try:

is_function<remove_reference<decltype(*pmain)>::type>::value 

btw: iso c++ forbids take address of ::main()