I want to create a constexpr struct which holds a number of states in an array, represented by state_type_t. The struct should be created dynamically via a parameter pack. My problem is that I don't know the size of the array holding the states as I would have to be aware of the number of arguments in the parameter pack... Is there a way around this (C++11)?

template<int S>
struct state_collection
{
    state_collection(state_type_t... Args) : states_(Args...) const noexcept {

    }

    std::array<state_type_t, S> states_; // <-- how big is S? How to derive S from parameter pack size?
};

struct region
{
    constexpr state_collection req_;
    constexpr state_collection act_;
};


region( { .req_{LOCAL_STATE_A, LOCAL_STATE_B}, .act_{} } );