weakref

A weakref holds a non-owning reference to a datum. The datum can be referenced again using resolve().

To figure out why this is important, you must understand how deletion in BYOND works.

Imagine a datum as a TV in a living room. When one person enters to watch TV, they turn it on. Others can come into the room and watch the TV. When the last person leaves the room, they turn off the TV because it's no longer being used.

A datum being deleted tells everyone who's watching the TV to stop. If everyone leaves properly (AKA cleaning up their references), then the last person will turn off the TV, and everything is well. However, if someone is resistant (holds a hard reference after deletion), then someone has to walk in, drag them away, and turn off the TV forecefully. This process is very slow, and it's known as hard deletion.

This is where weak references come in. Weak references don't count as someone watching the TV. Thus, when what it's referencing is destroyed, it will hopefully clean up properly, and limit hard deletions.

A common use case for weak references is holding onto what created itself. For example, if a machine wanted to know what its last user was, it might create a var/mob/living/last_user. However, this is a strong reference to the mob, and thus will force a hard deletion when that mob is deleted. It is often better in this case to instead create a weakref to the user, meaning this type definition becomes var/datum/weakref/last_user.

A good rule of thumb is that you should hold strong references to things that you own. For example, a dog holding a chew toy would be the owner of that chew toy, and thus a var/obj/item/chew_toy reference is fine (as long as it is cleaned up properly). However, a chew toy does not own its dog, so a var/mob/living/dog/owner might be inferior to a weakref. This is also a good rule of thumb to avoid circular references, such as the chew toy example. A circular reference that doesn't clean itself up properly will always hard delete.

Proc Details

resolve

Retrieves the datum that this weakref is referencing.

This will return null if the datum was deleted. This MUST be respected.