SFML Game Development book - bug in the sources?

[xqbt]

So I am reading a book called SFML Game Development (and I really like it), but I think I might have found a major memory leak in the provided sources. If you go to the main repository and check this file:
https://github.com/SFML/SFML-Game-Development-Book/blob/master/10_Network/Include/Book/SceneNode.hpp
you will see that there is no virtual destructor declared. I suppose that's a bug.
Please, fix me if I am wrong.

[Nexus]

The base classes sf::Transformable and sf::Drawable have a virtual destructors.

[xqbt]

OK, got it, thank you. It was dumb of me not to think of that.

[Laurent]

Isn't it a good practice to explicitly declare a destructor virtual for an abstract base class, regardless of its own parents? It's clearer for users, and less prone to errors when the code evolves (the parent classes may change, or not be parents anymore). It's like not including a standard header, because you know that some other that you already include does it

[Nexus]

It arguably is.

Declaring ABC destructors virtual can make sense, the same way that e.g. declaring constructors explicit by default or using override can. It's redundant, but helps prevent errors when migrating code.