ZScript: "final" keyword

[Player701]

What exactly does "final" do in ZScript? For all this time, I simply assumed that it could be used on overridden methods so that they cannot be overridden again in subclasses. I never actually bothered to check, since I didn't try to override them myself, and the code compiled just fine. However, now that I've run some tests, it seems that this keyword does not actually do anything at all. Does anyone know what its true purpose is?

In gzdoom.pk3, this keyword is encountered only twice, both times in zscript/actors/doom/scriptedmarine.zs:

Code: Select all

final void SetWeapon (int type)
{
    ...
}

final void SetSprite (class<Actor> source)
{
    ...
}

This makes no sense to me, since even if I assume that "final" doesn't work due to a bug, there is no point in using it on non-virtual methods anyway (since they cannot be overridden in the first place). My only reaction to this as of now is "WTF?"...

[phantombeta]

It seems it was supposed to do that, but no one ever coded it to. Other code does implicitly mark things as non-overridable (specifically, static and action), and the code does seem to handle it, so why the "final" keyword doesn't actually mark things as non-overridable is probably a mystery.

[Apeirogon]

According to definition, it must prevent virtual functions from overriding
https://github.com/coelckers/gzdoom/blo ... ypes.h#L23
And here is the confirmation
https://github.com/coelckers/gzdoom/blo ... .cpp#L2957

So.....its a bug and typo in scripted marines(functions was virtual before?)????

[Player701]

OK, so I guess maybe this should be moved to Bugs... And since those two functions in ScriptedMarine are not virtual, "final" should be removed from there, and its use on non-virtual functions should probably be made a compiler error. Well, at least that's what I'd do...

[Graf Zahl]

This was once working, I can't say what broke it.

[Rachael]

OK, so I guess maybe this should be moved to Bugs...

done

[phantombeta]

This was once working, I can't say what broke it.

It's not working because...
... There's no code for it. The token, modifier and compiler flag are defined, but it never sets the VARF_Final flag if the ZCC_Final modifier is set. Should be a trivial fix, I think.
I could definitely do it myself, but I'd need to know whether it should only be allowed on virtual functions first. IMO it should, but I think Graf should have the final say on that.

Btw, there's another modifier that's in the same situation as this one, "latent". But that one doesn't seem to have any backing flag in the compiler for it. I have the feeling it was something randi was planning for ZScript but you removed or something.

[Graf Zahl]

"Latent" was never implemented. One piece of trivia you should know is that the language was supposed to mimic UnrealScript, which is where this came from. But considering how the VM works, especially with a JIT in the game, this is a concept that's not really implementable anymore.

This isn't the only concept I removed. Another one was exceptions - but that put such an incredible drag on the VM that I decided early in the game not to pursue it. Even most experienced programmers I know have difficulties using exceptions right, no matter whether on Java, C++ or any other languages. ZDoom is really the only piece of software I know that uses exceptions properly, i.e. to report errors that need to be dealt with in a centralized spot. In basically all other cases they are the programming equivalentof a landmine and better avoided.