Does every variable have the UPROPERTY() mark?

anonymous_user_ad9223cf · February 4, 2018, 2:34pm

Hi, I’m checking out the garbage collection section at the C++ Programming Guide.

I’ve reached the section where it says: that any property without the UPROPERTY() mark it’ll be deleted by the garbaged collector because it’s not in the root set.

Does this mean I need to use this mark in every variable or otherwise it’ll just be deleted by the GC?

Thanks

anonymous_user_210522a1 · February 4, 2018, 3:46pm

No it is not required for every variable, only for those that need to be visible for UE. For example if you want to have a variable editable in the UE editor it needs to be a UPROPERTY, but if it is just a internal varaible for a class it is not required.

anonymous_user_ad9223cf · February 4, 2018, 4:30pm

but then won’t it be deleted by the garbage collector? as the documentation says? or is that just for objects?

anonymous_user_210522a1 · February 4, 2018, 5:11pm

GC wont touch non uproperty I think. I use a lot of non uproperty floats.

anonymous_user_ad9223cf · February 4, 2018, 6:05pm

I think what I’m referring to are UObjects and I’m just mistaking it with normal variables, could it be?

anonymous_user_ad9223cf · February 4, 2018, 10:12pm

Why is that?

anonymous_user_210522a1 · February 4, 2018, 10:03pm

If it is not a pointer to a UOBject but a value it can very well be a requirement to have the uproperty mark

anonymous_user_210522a1 · February 4, 2018, 10:23pm

At this point I am not sure, but since a UObject cán be created on the heap it is a problem if its value gets out of scope, because then you can’t deallocate it’s memory. The GC probably does that for you if it is a UPROPERTY. if you have a pointer (on the stack) to it, and it goes out of scope the pointer is deallocated by c++, and the GC would take care of the UObject (if needed) since all uobject values would be uproperty then.

anonymous_user_210522a1 · February 4, 2018, 10:28pm

To more specificly answer your question about GC: “In a nutshell, Garbage Collection (GC) traverses the object hierarchy through designated UPROPERTY’s, starting from the root objects (hence AddToRoot and RemoveFromRoot methods). Any object that cannot be reached through this traversal will be garbage collected. Accordingly, non-UPROPERTY variables are not counted by the GC system.” (A new, community-hosted Unreal Engine Wiki - Announcements - Epic Developer Community Forums)

So UPROPERTY means it can be GCed if there is no reference to it, a non uporpterty can’t

anonymous_user_ad9223cf · February 5, 2018, 5:11pm

okay got it! thank you ^^

it_makes · November 20, 2021, 4:30pm

As i understood, actually UPROPERTY macro ensures that the object declared in the pointer is
considered to be referenced, that means, that property with that macro WON’T be garbage-collected.