Inheritance from Print class with no virtual destructor

[smartynov]

I'm trying to create a library that uses PubSubClient. I create a mqttClient = new PubSubClient on initialization and I want to delete mqttClient in some cases. However, my compiler (platformio) issues a warning "deleting object of polymorphic class type 'PubSubClient' which has non-virtual destructor might cause undefined behaviour [-Wdelete-non-virtual-dtor]".

As far as I understood the cause for this warning is that PubSubClient class is inherited from Print class, and there is no virtual destructor in Print class. This is discussed in arduino/Arduino#4466 – this PR exists from 2016, however it is still not merged.

While most accurate solution will be adding virtual destructor to Print base class, I can't see any advantages for PubSubClient to be derived from Print class. I suggest to remove this inheritance and get rid of undefined behaviour.

[knolleary]

The addition of the Print class was done here #494 by @amcewen as part of the large message api changes.

Removing the inheritance will certainly break existing sketches that make use of it, so no, we can't just remove it.

[smartynov]

Ok, I understand. The sad part is that Arduino maintainers aren't going to fix this issue with Print either. So I can see no clean solution here...