variable no of arguments for class template's member function - c++

Question

I am just learning about templates and was trying to write a simple template class for vectors like
template <unsigned N>
struct vec {
std::array<float, N> m_buffer;
float& operator[](unsigned index) { return m_buffer[index]; }
vec(float value) { std::fill(m_buffer.begin(), m_buffer.end(), value); }
vec(float(&value)[N]) { std::copy(std::begin(value), std::end(value), std::begin(m_buffer)); }
vec(float* value) {
for (int i = 0; i < N; i++)
m_buffer[i] = value[i];
}
float getmag() {
float ret=0;
for (int i = 0; i < N; i++)
ret += m_buffer[N] * m_buffer[N];
return sqrt(ret);
}
};
int main() {
vec<3> a({ 1.0f, 2.0f, 3.0f });
return 0;
}
now I want to make a contructor that will take N number of floats and assign them to the array m_buffer but did not find any ways.
This could be done for certain values of N by specializing the template class but how will one do for any number of N?

Answer 1

You might use variadic template:
template <unsigned N>
struct vec {
std::array<float, N> m_buffer;
template <typename ... Ts>
vec(Ts... args) : m_buffer{{args...}} {}
// ...
};
SFINAE might be added to check arity and to restrict to float convertible parameters.
Alternative which might be appropriate is usage of index_sequence:
template <typename T, std::size_t>
using always_t = T;
template <typename Sequence> struct vec_seq;
template <std::size_t ... Is>
struct vec_seq<std::index_sequence<Is...>>
{
static constexpr std::size_t N = sizeof...(Is);
std::array<float, N> m_buffer;
vec_seq(always<float, Iss... args) : m_buffer{{args...}} {}
// ...
};
template <std::size_t N>
using vec = vec_seq<std::make_index_sequence<N>>;