The using declaration modifies your namespace.

From the docs:

    namespace X
    {
        using ::f;        // global f is now visible as ::X::f
        using A::g;       // A::g is now visible as ::X::g
    }
 
    void h()
    {
        X::f(); // calls ::f
        X::g(); // calls A::g
    }

Link to docs: https://en.cppreference.com/w/cpp/language/namespace#Using-d...