Why does `endl` working fine without namespace `std`?

Question

Case 1:

#include <iostream>
int main() 
{
   std::cout<<"Hello World"<<endl;
      return 0;
}

Compiler give an error because endl need namespace std like std::endl.

case 2:

#include <iostream>
int main() 
{
      endl(std::cout); 
      return 0;
}

But, In second case without namespace std, endl working fine. Demo.

Why does endl working fine without namespace std?