> 2. modifying how things are printed requires modifying global state This only applies to std:: cout and std::cerr. Other stream interfaces, like std::fstream

> 2. modifying how things are printed requires modifying global state This only applies to std:: cout and std::cerr. Other stream interfaces, like std::fstream or std::stringstream don't have this problem. Also, it is orthogonal to operator overloading.