Pass a variable number of arguments into a function - c++

Question

I know how to use variadic templates and ellipses to accept a variable number of arguments, but how do you pass a variable number of arguments into a function?
Take the following code for example:
#include <iostream>
struct A {
A(int a, int b) : x(a), y(b) {}
int x, y;
};
struct B {
B(int a, int b, int c) : x(a), y(b), z(c) {}
int x, y, z;
};
template<typename T, typename... TArgs>
T* createElement(TArgs&&... MArgs) {
T* element = new T(std::forward<TArgs>(MArgs)...);
return element;
}
int main() {
int Aargs[] = { 1, 2 };
int Bargs[] = { 1, 2, 3 };
A* a = createElement<A>(Aargs); //ERROR
B* b = createElement<B>(Bargs); //ERROR
std::cout << "a.x: " << a->x << "\na.y: " << a->y << "\n" << std::endl;
std::cout << "b.x: " << b->x << "\nb.y: " << b->y << "\nb.z: " << b->z << "\n" << std::endl;
delete a;
delete b;
}
Is there any way to expand the arrays so that each of their values is like an argument being passed to the function (similar to parameter pack expansion)?
Or, if not, is there any other way to make this work?

Answer 1

You can expand the array using a std::index_sequence
#include <iostream>
#include <utility>
struct A {
A(int a, int b) : x(a), y(b) {}
int x, y;
};
struct B {
B(int a, int b, int c) : x(a), y(b), z(c) {}
int x, y, z;
};
template<typename T, typename... TArgs>
T* createElement(TArgs&&... MArgs) {
T* element = new T(std::forward<TArgs>(MArgs)...);
return element;
}
template<typename T, typename U, size_t... I>
T* createElementFromArrayHelper(std::index_sequence<I...>, U* a){
return createElement<T>(a[I]...);
}
template<typename T, typename U, size_t N>
T* createElementFromArray(U (&a)[N]){
return createElementFromArrayHelper<T>(std::make_index_sequence<N>{}, a);
}
int main() {
int Aargs[] = { 1, 2 };
int Bargs[] = { 1, 2, 3 };
A* a = createElementFromArray<A>(Aargs);
B* b = createElementFromArray<B>(Bargs);
std::cout << "a.x: " << a->x << "\na.y: " << a->y << "\n" << std::endl;
std::cout << "b.x: " << b->x << "\nb.y: " << b->y << "\nb.z: " << b->z << "\n" << std::endl;
delete a;
delete b;
}