On Fri, 12 Jul 2024 at 20:08, Dalbey, Keith <kdal...@sandia.gov> wrote:
>
> The means by which this FIX was implemented caused OTHER problems
>
> template <typename F, typename S>
> std::ostream& operator<<(std::ostream& os, const std::pair<F,S>& pr)
> {
> os << "(" << pr.first << ", " << pr.second << ")";
> return os;
> }
>
> Will only work for CONCRETE classes that take the place of "F" and "S" IFF
> each of their concrete operator<< 's is FORWARD DECLARED ahead of the above
> template, so primitives like int and double should still work, but if you
> include this file in a header file that contains a concrete class that you
> define an operator<< for, and then use in another file, you're SOL.
This is simply not true.
#include <ostream>
#include <utility>
template <typename F, typename S>
std::ostream& operator<<(std::ostream& os, const std::pair<F,S>& pr)
{
os << "(" << pr.first << ", " << pr.second << ")";
return os;
}
namespace ns {
struct A { };
inline std::ostream& operator<<(std::ostream& out, const A& a)
{
return out << "A\n";
}
}
#include <iostream>
int main()
{
std::pair<int, ns::A> p{};
std::cout << p;
}
This program works via ADL, because it uses namespaces correctly.
If you dump all your operator overloads in the global namespace, then
it doesn't work. So don't do that then.
