How to dynamically narrow a union type on a class property?

[nilmerg]

Given the following: https://phpstan.org/r/c67364ca-0153-440a-92c3-edb5075bf3d2

How can I solve the error? I tried object shape syntax, but since my type is not object or stdClass, this doesn't seem to work.

[ondrejmirtes]

Only idea I have for you: https://phpstan.org/r/7edd9a15-7d4d-4b72-8ecc-2ff57a7a2238

Or make two different Foo classes - one for A and another for B.

[nilmerg]

Thanks. I'd have liked to avoid re-assignment, but if that's the only option I'll take it.