Updated the assert checking Dict versions

[eulerkochy]

Changed the assert in code, to incorporate a check on versions of the Dict

[KristofferC]

What was the reason you closed the previous PR https://github.com/JuliaLang/julia/pull/31097/files (that had the same changes as here)

Please try to keep working on the same PR instead of opening a new one. By reopening a new one the discussion on the earlier one is lost.

[eulerkochy]

There were a lot of unwanted commits in that PR. I just tried to submit a 'clean' PR this time! Sorry for the inconvenience!
I'll take care of it from the next time!

[KristofferC]

You can always update an existing PR no matter how bad you mess it up.

[vtjnash]

vtjnash: this a valid assert or should it be an error?

Is is a valid use of assert. If you follow the logic of the above function, it is logically impossible to happen, without memory corruption (however that could happen during race-y multithreading code—or equivalents such as finalizers and generator functions—hence the assert to kill the program).

[eulerkochy]

error thrown is suggestive of such an event, at least it gives a reason why the program will get terminated due to mismatch of age of the Dict

[KristofferC]

Yes but we want this to be an assert to allow it to potentially be removed in the future at some optimization level. That's the point of @assert over error.

[KristofferC]

Closing since the assert is valid (#31110 (comment))