#include <iostream>
#include <optional>
#include <functional>
using namespace std;
class A
{
public:
  A(const A& a){cout<<"copy"<<endl;}
  A(){}
};
void foo(std::optional<A> a)
{

}

int main()
{
    A a;
    foo(nullopt);
    foo(a);
    return 0;
}