问VSCode说std：：operator<<过载时时间不明确

EN

#include <chrono>
#include <iostream>

// marks chrono as ambiguous
using std::chrono::milliseconds;

namespace std {
namespace chrono {

// again marks chrono as ambiguous
template <class U, class T>
std::ostream& operator<<(std::ostream& os, const typename ::std::chrono::duration<U, T>& dur) {
  os << "foo";
  return os;
}

}  // namespace chrono
}  // namespace std

namespace example {

void DoThing() {
  // NOT marked as ambiguous
  milliseconds x(10);
  // Says no match for operator<< and milliseconds
  std::cout << x;
}

}  // namespace example