JavaScript switch statement in Unity

Unity Engine
1

This function won’t compile with the switch statement in it:

function isHostile( t : Rocket ){
	if( faction == t.faction ){
		return false;
	}
	
	switch ( faction ){
		case factionEnum.neutral:
		case factionEnum.goodAncient:
			return false;
			break;
		case factionEnum.legion:
		case factionEnum.solenoid:
		case factionEnum.human:
		case factionEnum.arkane:
			if( t.faction == factionEnum.pirate ) return true;
			if( t.faction == factionEnum.evilAncient ) return true;
			return false;
			break;
		case factionEnum.pirate:
		case factionEnum.evilAncient:
			return true;
			break;
	}
}

Is switch implemented at all in UnityScript?

2

Yep; I think all the case statements need a matching break statement though, even if they don’t do anything.

–Eric

3

I don’t think you need the breaks since you have a return. And I think it’s ok to pile cases as you did, that’s the point of a switch.
All this I know for sure from C#, but I guess JS is the same.

I’d try to compile it to see what’s wrong but I don’t feel like re-writing your enum :sweat_smile:

4

Nope, just tested with a very similar switch statement I wrote…you can’t do stuff like

      case factionEnum.human: 
      case factionEnum.arkane: 
         if( t.faction == factionEnum.pirate ) return true; 
         if( t.faction == factionEnum.evilAncient ) return true; 
         return false; 
         break;

You have to write something for factionEnum.human, even if it’s just break. This makes it not like real Javascript, where you can stack cases.

–Eric

5

Yep, doesn’t seem normal… you should probably report it.

6

In fact, you can’t do it in C#, either. You get “error CS0163: Control cannot fall through from one case label to another” if you try. Maybe you’re thinking of C/C++, in which falling through from one case to another is allowed.

EDIT: just found this useful page, which tells you how to explicitly fall through cases in C#. Don’t know if that works for Javascript, though. I seem to recall that Unity’s Javascript doesn’t have goto at all.

EDIT 2: and after all that, I can’t get the fallthrough behaviour described above to work for code compiled with the command line Mono tools. I haven’t tried it in Unity itself, but I expect it will behave in the same way. Maybe this is something that Mono doesn’t implement in the usual way.

7

Really? Without stacking cases, switch statements are no more useful than chained if/elses. :confused:

8

To NCarter: scroll to the bottom of the page you just sent:

If it doesn’t work in Unity’s C#, it’s probably Mono’s fault. Same with JS, should work, but OTEE’s implementation is still incomplete.

Also, to podperson, last paragraph of that same page:

As a result of the C# rules requiring explicit flow-control to occur at the end of a case block (most usually a break), many people question why the behavior simply wasnt changed such that fall-through didnt occur.  That is, dont make break required, simply change the semantics of switch to not have fall-through for cases.  The reason this wasnt done was so that developers who were very used to C++ wouldnt have a hard time understanding what a switch statement was doing.

So writing

return false;
break;

is an overkill: return already is a flow-control keyword.

9

Oops, I just realised that I accidentally omitted the break statement in the final case (!), and that was why it wasn’t working for me. Therefore, that page I linked is indeed correct for C# with Mono/Unity, and you were right in the first place.

I thought it was odd that the Mono guys had missed something fundamental like that. :slight_smile:

10

You bet! Now that I think about it, the whole system would probably crash, as a zillion functions must be relying on switch!..

11

Wow this is an old post… nether the less… i think i found a work around…

in javascript:

var value : int;

function Update(){
	
	switch(value){
		case 0:; // fall through
		case 1:; // fall through
		case 2:
			print("I can handle case: " + value);
			break;
		default:
			print("I can not handle case: " + value);
			break;
	}
}

Simply putting a line enders after the case, stops it from complaining and makes it work