The scalar product of two vectors with size 'N' defined as SP(a, b) = a_1 * b_1 + ... + a_N * b_N.
Compile-time integer vector defined as:
template<int... I>
struct Vector;
Function product interface:
template<typename Vector1, typename Vector2>
constexpr int product
For example, following code could be used for test:
static_assert(product<Vector<1, 2, 5>, Vector<1, 3, 4>> == 27);
How can product be implemented to match the assert and interface above?
With C++17 folding
template <int...>
struct Vector
{ };
template <typename, typename>
constexpr int product = -1;
template <int ... Is, int ... Js>
constexpr int product<Vector<Is...>, Vector<Js...>> = (... + (Is*Js));
int main ()
{
static_assert(product<Vector<1, 2, 5>, Vector<1, 3, 4>> == 27);
}
Maybe something like this:
template<int ... >
struct Vector{};
template<int ... Idx1, int ... Idx2>
constexpr int product(Vector<Idx1...>, Vector<Idx2...>) {
static_assert(sizeof...(Idx1) == sizeof...(Idx2), "Product cannot be calculated, dims dismatched");
int res = 0;
int temp [] = { (res += (Idx1 * Idx2),0)...};
static_cast<void>(temp);
return res;
}
int main() {
static_assert(product(Vector<1,2,5>{},Vector<1,3,4>{}) == 27);
}
Without C++17 fold expressions, by using function overloading.
template <int... Ele>
struct vector {};
template <int Ele1, int Ele2>
constexpr int DotProd(vector<Ele1> v1, vector<Ele2> v2) {
return Ele1 * Ele2;
}
template <int Ele1First, int... Ele1, int Ele2First, int... Ele2>
constexpr int DotProd (vector<Ele1First, Ele1...> v1, vector<Ele2First, Ele2...> v2) {
return (Ele1First * Ele2First) + DotProd(vector<Ele1...>{}, vector<Ele2...> {});
}
int main() {
vector<1, 2, 3, 4> v1;
vector<4, 3, 2, 1> v2;
static_assert (DotProd(v1, v2) == 20);
return 0;
}