[damon_dam]

I don't really disagree with what you wrote. To expand upon my argument, the issues you mention can also be self-policed, or maybe enforced with higher safety levels of the presumptive -W20 switch:

- No reference variables in user code (reference parameters are OK.)

- Any classes that hold reference member variables can only be instantiated on the stack. The objects the references refer to must either be stack objects or reference parameters to the instantiating function.

- For durable links to sub-objects, use handles (tuples of std::shared_ptr to the main object plus a sub-object link or identifier.)

- Alternatively, require externally-accessible sub-objects to be held in shared_ptr's by the main object. They can then have superset lifetimes when needed.

I'll stick to the memory safety topic, but similar solutions exist for some of the other topics you mention, e.g. by avoiding std::optional.