Thank you. I don't need any of those, though. $immutable->getAttr() is easy to mock, easy to override, and allows for custom behavior (e.g. return clone $this->Attr).

Static return type, useful but since I use interfaces for everything it's not really needed. Union types, also not really needed because either 2 interfaces share a common ancestor or I'll have separate methods for different types. But most of the time, I encapsulate things behind interfaces that do one thing, so having different methods per type can often be avoided.

Named arguments are a pain for me since now I can't change parameter names anymore. This is particularly annoying with different coding styles in dependencies vs my own code. My code ends up not conforming to the coding standard that I've used since it was introduced (PSR-2R).

Exceptions as expressions is a nice to have, but exceptions in general are a thing to avoid doing. Not that things can't go wrong, not that chugging along in the face of errors is good, of course it's not. But if you have a lot of exceptions in your code, that's a smell of bad design. I've got 13 different exceptions used 20 times in total, over 4683 LoC on my current project. Mostly, whenever one of them is triggered, whatever I changed last was incomplete and led to an inconsistent configuration.

That said, your use case for PHP is probably very different. Especially since I don't care much at all about performance anymore. I used to, but CPUs are so much faster nowadays and PHP itself has improved.