namespaces, classes and free functions - when do you need fully qualified names

Question

In my example below, why do I have to fully qualify the name of the free function in the cpp to avoid linker errors and why does it work for the class function without? Can you

Answer 1

If you don't qualify FreeFunction definition, the compiler does not know for sure anther you want to provide implementation for the previously forward-declared Test::FreeFunction or for a separate FreeFunction in the current namespace.

On the other hand, there's only one way to resolve the name CTest - as the class definition from the Test namespace. Thus, there's no need to fully qualify it.

However, if the CTest name resolution is ambiguous (say there's another CTest class in the current namespace as well), you will have to fully qualify the method declarations.