I have the following code, and I can move unique pointer variable several times.
Why is it allowed? Also, what is the difference between an arg with && and without `&&?

#include <iostream>

std::unique_ptr<int> make_obj(int v) {
  return std::make_unique<int>(v);
}

void print(std::unique_ptr<int> &&v) { // <- why && allows multiple moves?
  std::cout << *v << std::endl;
}

int main() {
  auto val = make_obj(1);
  print(std::move(val)); // the first time move
  int a = 0;
  print(std::move(val)); // the second time move
}