Namespaces and Operator Overloading in C++

Question

When authoring a library in a particular namespace, it's often convenient to provide overloaded operators for the classes in that namespace. It seems (at least with g++) that the overloaded operators can be implemented either in the library's namespace:

namespace Lib {
class A {
};

A operator+(const A&, const A&);
} // namespace Lib

or the global namespace

namespace Lib {
class A {
};
} // namespace Lib

Lib::A operator+(const Lib::A&, const Lib::A&);

From my testing, they both seem to work fine. Is there any practical difference between these two options? Is either approach better?

question from:https://stackoverflow.com/questions/171862/namespaces-and-operator-overloading-in-c

Answer 1

You should define them in the library namespace. The compiler will find them anyway through argument dependant lookup.

No need to pollute the global namespace.