The GUI Local Variable Trick

06-26-2008, 07:40 AM

So anyone who has used GUI probably knows about that weird, random trick you can do to make globals act like locals in GUI. For those of you don't, here's what it looks like:

Trigger:

Events

Unit - A unit starts the effect of an ability

Conditions

Actions

Custom script: local unit udg_MyUnit

Set MyUnit = (Triggering Unit)

Wait 2.00 game-time seconds

Unit - Kill MyUnit

Custom script: set udg_MyUnit = null

(MyUnit being a unit variable created in the Variable Editor.)

Anyway, what I'm wondering is this: why does it work? Do we have any clue what this does to the parser to make it work, because it seems like if it was compiled normally it simply wouldn't compile and it would look like:

JASS:

function Trig_MyTrigger_Actions takes nothing returns nothing
    local unit udg_MyUnit
    set udg_MyUnit = GetTriggerUnit()
    call PolledWait(2.00)
    call KillUnit(udg_MyUnit)
    set udg_MyUnit = null
endfunction

And one more question: does this bug still work if you're using the NewGen pack?

06-26-2008, 07:47 AM	#2
Pheonix-IV	It works because by using the script "Local unit udg_MyUnit" you're defining the variable udg_MyUnit as a local unit variable. However, that definition doesn't occur until the game runs, so the variable appears to be global.

06-26-2008, 07:51 AM	#3
Pyrogasm	Okay, that makes sense... but why doesn't it generate a syntax error?

06-26-2008, 07:56 AM	#4
Jazradel	Just a bug with the syntax error. Something to do with the way it handles scope, presumably. As an interesting side note, doing that with an array does cause a syntax error.

06-26-2008, 08:29 AM

cohadar

There are 2 udg_MyUnit variables, one local and one global.

It compiles somewhat like this:

JASS:

globals
    unit udg_MyUnit
endglobals

function Trig_MyTrigger_Actions takes nothing returns nothing
    local unit udg_MyUnit
    set udg_MyUnit = GetTriggerUnit()
    call PolledWait(2.00)
    call KillUnit(udg_MyUnit)
    set udg_MyUnit = null
endfunction

and since local variables take precedence over globals ones global variable is never used inside Actions (but still exists)
In fact if you would to remove the local unit udg_MyUnit from the beginning of action the action would be using global variable (no-mui)

06-26-2008, 08:48 AM	#6
Captain Griffen	JASS == voodoo

06-28-2008, 05:32 PM	#7
Kyrbi0	Y'know, I always confuse Pyrogasm and Phoenix-IV.

06-28-2008, 08:59 PM	#8
Pyrogasm	Well then, if it's such a simple syntax thing... why doesn't it work for more than one variable per function...?

06-28-2008, 09:18 PM	#9
Captain Griffen	Voodoo. Blizzard's defensive programming is awful. It's probably a bug in their compiler that it works at all.

06-29-2008, 07:30 AM

#10

cohadar

Quote:

Originally Posted by Pyrogasm

Well then, if it's such a simple syntax thing... why doesn't it work for more than one variable per function...?

Make a simple test map, compile it, go to logs/inputwar3map.j and tell us.

06-29-2008, 08:11 AM	#11
Pheonix-IV	I'm going to go with Griffen's explanation. It's Voodoo, a Wizard probably did it, or at least was responsible for it.

06-29-2008, 09:11 AM	#12
Gorman	Wizards dont do voodoo.

06-29-2008, 11:40 AM	#13
MaD[Lion]	not voodoo, just bad programming :P

06-29-2008, 02:13 PM

#14

Vexorian

Quote:

Originally Posted by Pyrogasm

Well then, if it's such a simple syntax thing... why doesn't it work for more than one variable per function...?

Blizz probably screwed up when they hacked it so it becomes non-case sensitive. There could be an off by one error or something like that, no idea.

BLizz were intending GUI people to do global shadowing like this, they even hacked the compiler so it becomes non-case-sensitive after you do that, so GUI guys don't have to bother with correct capitalization...

06-30-2008, 08:24 AM

#15

cohadar

Quote:

Originally Posted by Vexorian

If they were so good to GUI guys why they did not add Remove functions to GUI.