Best practice for overloading functions with only STL types-CodePudding

I would like to overload operator<<(std::ostream&, std::chrono::duration<std::uint64, std::nano>) - and ideally without requiring users to write using statements everywhere.

What's the best practice here?

Context...

// Replace code like this:
using Time = std::uint64_t;
void example(Time ts) {
    if (ts) { std::cout << ts; }

}

// with code like this:
using Time = std::chrono::duration<std::uint64_t, std::nano>;
void example(Time ts) {
    if (!!ts) { std::cout << ts; }
}

// this 'works for me'; but it is not allowed to add overloads to `namespace std`
// The type `Time` can be used in any other namespace, and the operators are found by ADL
namespace std {
    ostream& operator<<(ostream&, chrono::duration<uint64_t, nano>);
    bool operator!(chrono::duration<uint64_t, nano>);
}

Is there a way to get the effect of placing the overloads in the std namespace without breaking the rules on extending namespace std?

CodePudding user response：

You put it in the global namespace. Any function outside of namespace std that does name lookup for << will find your overload, and prefer it to the one defined in C 20.

Afaict, the only place where this fails is std::ostream_iterator, as that is the only call to << within namespace std.

See it on coliru