Pass container to a variadic template function

Question

In modern C++17, how can we pass a container such as std::vector to a variadic template function in below code?

template <typename... Args>
void foo(const Args&... args) {
    for (const auto& arg : { args... })
        std::cout << arg << ' ';
}

int main() {
    foo(1, 2, 3);
    std::vector vec{ 1, 2, 3 };
    foo(vec);
}

A similar question has been already asked: https://stackoverflow.com/a/49025839/11857122 but that solution uses a SFINAE. Can we omit that mechanism and use something easier like if constexpr etc.?

Answer 1

Taking your comment into consideration, this is how you can adapt your code to print the elements of the vector

#include <iostream>
#include <vector>

template <typename... Args>
void foo(const Args&... args) {
  for (const auto& arg : {args...}) {
    std::cout << arg << ' ';
  };
}

template <typename T>
std::ostream& operator<<(std::ostream& o, const std::vector<T>& v) {
  for (const auto& x : v) {
    o << x << ' ';
  }
  return o;
}

int main() {
  foo(1, 2, 3);
  std::vector vec{1, 2, 3};
  foo(vec);
}

Output

1 2 3 1 2 3