structured_binding_get_2.cpp

template<std::size_t idx> auto get(const B &b)
{
    static_assert (idx < 4);
    if constexpr (idx == 0) {
        return b.a;
    } else if constexpr (idx == 1) {
        return b.c;
    } else if constexpr (idx == 2) {
        return b.d;
    } else {
        return b.e;
    }
}