I often wonder how this would map to other languages (as C++ often entails complexity and clever work arounds such as this article).

In Java or C# (and of course in C++), you could have a token system where the token can only be provided by Device :

VFS: void register(DeviceToken):

DeviceToken: empty interface (marker)

Device: private DeviceToken provideDeviceToken();

This hides both VFS and Device classes from accessing each others' private members.

You can also constrain how gets to provide DeviceToken by adding sufficient comments in code.