C++ STL type_traits question

Question

I was watching the latest C9 lecture and noticed something interesting..

In his introduction to type_traits, Stephan uses the following (as he says, contrived) example:

template <typename T> void foo(T t, true_type)
{
    std::cout << t << " is integral";
}
template <typename T> void foo(T t, false_type)
{
    std::cout << t << " is not integral";
}

template <typename T> void bar(T t)
{
    foo(t, typename is_integral<T>::type());
}

This seems to be far more complicated than:

template <typename T> void foo(T t)
{
    if(std::is_integral<T>::value)
        std::cout << "integral";
    else
        std::cout << "not integral";
}

Is there something wrong with the latter way of doing it? Is his way better? Why?

Thanks.

Answer 1

Basically first option uses knowledge about "integrality" of the type at compile-time and the second option - moves this knowledge to run-time.

This means that we may use for integral types code which is not compilable for non-integral types.