serialization and TMap: why does this compile?

Development Programming & Scripting C++
1

This page claims: “Caveat: Unlike TArray, TSets (and TMaps) are not directly supported as UPROPERTYs and so cannot be automatically replicated, serialized, etc…” and “Like the TSet, the TMap cannot be declared as a UPROPERTY.”

Thus I was surprised to write this line of code inside a UCLASS for a faction system and discover that it compiles just fine:



   UPROPERTY()
   TMap<const UPlayerFaction*, float> FactionAttitude;

Is that documentation page out of date? Or is it that I’ll suffer horrible attacks from subtle save/load bugs later on if I try to use that for game serialization?

Certainly I could go write my own serializer for the map data, but I’d rather not if I don’t have to!

2

Yes it’s out of date, it’s been in since 4.8.
You still can’t expose it properly in the editor, but serialization and garbage collection are handled.

3

Sweet! Thanks Kamrann.

4

I don’t believe that serialization is handled correctly just yet - I have experimented in 4.9.1 with saving a level containing an actor with a TMap UPROPERTY, and on re-load the TMap was empty. Switched to a TArray and it was all dandy.

5

Hmm okay, that’s surprising. I haven’t tested but I assumed serialization was done, since they didn’t mention it was missing. Anyway cheers, will look into it.

6

I’m not far enough along in my project to easily say whether it works, but at the least, I just looked and they have added an operator<<() in Runtime/Core/Public/Containers/Map.h. I’ll get around to trying it out in time I hope. Seems like it shouldn’t be all that hard to serialize a map or set, so I guess it either works or will be easy enough to fix.