[大小为N的两个向量的标量积定义为SP(a,b)= a_1 * b_1 + ... + a_N * b_N。
编译时整数向量定义为:
template<int... I>
struct Vector;
功能产品界面:
template<typename Vector1, typename Vector2>
constexpr int product
例如,以下代码可用于测试:
static_assert(product<Vector<1, 2, 5>, Vector<1, 3, 4>> == 27);
如何实现产品以匹配上面的断言和接口?
使用C ++ 17折叠
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);
}
也许像这样:
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);
}