Printing C++ Types with __PRETTY__FUNCTION__. You can use this C++ trick to explore what the compiler is doing to your types, either for metaprogramming purposes or just to learn more about auto, auto&&, and decltype(auto)

print_type.cpp

#include <cstdio>
template<typename T>
void f(void)
{
    puts(__PRETTY_FUNCTION__);
}
#define EXPLORE(expr) \
    printf("decltype(" #expr ") is ..."); \
    f<decltype(expr)>();

int main()
{
    auto x = 5;
    auto&& y = 5;
    decltype(auto) z = 5;

    EXPLORE(x); EXPLORE((x));
    EXPLORE(y); EXPLORE((y));
    EXPLORE(z); EXPLORE((z));
}