I have a variadic template and would to define the arguments using using alias declaration.
Here is an example:
template<class I, class... P>
struct Molecule {
using Index = I;
};
My question is, how can I define the first argument of P... ?
I have already tried this, but it generates an error:
template<class I, class... P>
struct Molecule {
using Index = I;
P array[sizeof...(P)] = { P... };
using Part1 = array[0];
};
Any suggestions please?
how i can define the first argument of P... ?
If the Molecule can be redefined to the following, you get it directly:
template<class I, class First, class... P> {
using Part1 = First;
// .....
}
Otherwise, make a trait to find the first type:
template<typename First, typename... Rest>
struct first { using type = First; };
template<typename... Args> using first_t = typename first<Args...>::type;
Now
template<class I, class... P> struct Molecule {
using Part1 = first_t<P...>; // first type
};
assuming that you would have at least one argument in variadic P....