I've noticed some problem with another hashlist that after adding about 2000 items to it, it starts to have problems. There are duplicates added (possibly a collision?)

Is there a such thing as a perfect hashlist which never has a collision, or will they always have problems... In that case a regular but slower List might be of use for perfection.

If there is an error would it throw an exception?

PM Lars wrote

Is there a such thing as a perfect hashlist which never has a collision,

No, there are infinite possible items you can add to a haslist, but only a finite number of available hashes.
It's the pigeon hole principle:
https://en.wikipedia.org/wiki/Pigeonhole_principle

Hash lists will always create collisions if enough elements are added. After all their purpose is to speed up the search thus they reduce the search space. This is by design.

If there should really be a problem with adding an element then an exception will be thrown.

Regards,
Sven

I've noticed some problem with another hashlist that after adding about 2000 items to it, it starts to have problems.

BTW, sorry to be more clear I meant I used another hashlist unit, not the contnrs one but another open source public domain one

This one:

https://github.com/z505/delphi-hashlist

And had problems with it.

I will try out contnrs one to compare soon!