## About The Pull Request
Replaces weakref usage in AI blackboards with deleting signals
All blackboard var setting must go through setters rather than directly
## Why It's Good For The Game
This both makes it a ton easier to develop AI for, and also makes it
harder for hard deletes to sneak in, as has been seen with recent 515
prs showing hard deletes in AI blackboards
(To quantify "making it easier to develop AI", I found multiple bugs in
existing AI code due to the usage of weakrefs.)
I'm looking for `@Jacquerel` `@tralezab` 's opinions on the matter, also
maybe `@LemonInTheDark` if they're interested
## Changelog
🆑 Melbert
refactor: Mob ai refactored once again
/🆑
ELEMENT_DETACH is **not** a requirement to having `Detach` called.
Detach is always called when the element itself is destroyed.
ELEMENT_DETACH is a flag that when set, makes sure Detach is called when
the atom destroys.
Sometimes you want this, for instance:
```dm
/datum/element/point_of_interest/Detach(datum/target)
SSpoints_of_interest.on_poi_element_removed(target)
return ..()
```
This Detach cleans up a reference that would have hung if target was
destroyed without this being called.
However, most uses of Detach are cleaning up signals. Signals are
automatically cleaned up when something is destroyed. You do not need
ELEMENT_DETACH in this case, and it slows down init. This also includes
somewhat more complex stuff, like removing overlays on the source
object. It's getting deleted anyway, you don't care!
I have removed all uses of ELEMENT_DETACH that seemed superfluous. I
have also renamed it to `ELEMENT_DETACH_ON_HOST_DESTROY` to make its
purpose more clear, as me and a lot of other maintainers misunderstood
what it did,
---
An update to this, ELEMENT_DETACH *is* needed for anything that can
register to a turf, as turfs do not clear their signals on destroy.
