C++ use symbols from other namespace without making them externally accessible

Question

Is there a construction similar to using namespace that doesn't make the imported symbols visible outside the body (or bodies) of the namespace?

In this example here, every symbol in whatever and other_namespace will be accessible through Foo::<name_of_symbol> as well ... and I'd like a way to prevent that from happening.

namespace Foo {
  using namespace whatever;
  using namespace other_namespace;
  // some definitions
}

As a complete example, this program is valid. If an alternative to using namespace with the intended semantics existed and were used, it would not be.

namespace a {
  int func(int x) {
    return 10;
  }
}

namespace b {
  using namespace a;
}

namespace c {
  int do_thing(int x) {
    return b::func(57);
  }
}

Answer 1

You can use an alias inside an unnamed namespace.

namespace a_long_namespace_name {
    void someFunc() {};
}

namespace b {
    namespace { // an unnamed namespace
        namespace a = a_long_namespace_name; // create a short alias
    }

    void someOtherFunc() {
        a::someFunc();
    }
}

b::a::someFunc(); // compiler error

You would still need to be writing the namespace to call a function, but it makes calls way shorter.