//test.cpp
#include <type_traits>

double* func() {}

static_assert(std::is_same<double*(*)(), decltype(func)>::value, "");

int main() {}

g++ -std=c++11 -c test.cpp

test4.cpp:6:1: error: static assertion failed:
static_assert(std::is_same<double*(*)(), decltype(func)>::value, "");
^

double* func() {}
auto ptr = func;

static_assert(std::is_same<double*(), decltype(func)>::value, "");
static_assert(std::is_same<double*(*)(), decltype(ptr)>::value, "");

int main() {}