[kazinator]

By definition, if avoiding something isn't possible, then there cannot be a "how to avoid".

Why even mention a non-starter choice, like using type punning through a void pointer, as an alternative to a forward declaration.

If a construct is "not possible to avoid" that generally means "not possible to avoid without changing the structure of code and run-time data (let alone changing them to something unsafe)".

Gratuitous forward declarations of C++ classes are "bad" for various reasons. Such as: people sometimes write them just to shut up the compiler, instead of including the right header to provide that declaration. "I'm just using a pointer to this; what's the harm."

It makes perfect sense for a coding standard to advise against this.