Static, nonmember or static nonmember function?

Question

Every time I have some functionality which is in the direction of \"utility\", I end up wondering which option is the best. For instance, printing message structs (own or extern

Answer 1

I use struct with static functions, because it offers a slighly better isolation than non-member functions in namespaces (due to the avoidance of Koenig lookup).

To give an example of the thing I want to avoid:

namespace Foo
{
      struct A
      {
      };

      void f(const A& a) {}
}

void f(const Foo:A& a) { std::cout << "AAA"; }

int main(void)
{
      Foo::A a;
      f(a); // calls Foo:f
      return 0;
}