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vJass Optimization: Using a First of Group Loop for Enumeration
Preface:
This guide is intended for experienced jass users who have a goal of optimized triggers in their maps. My aim is to create a short, concise, and targeted tutorial that is easy to follow and navigate.
My primary audience is users who know how to use the best method of enumeration prior to the 1.24 warcraft 3 update - a
The body of this article will be in example form, with only some minor explanation throughout.
Limitations:
The inherent idea of a First of Group loop is that the group is emptied each time it is used. This can be detrimental in the case that you want to save a group of units in a
Pre-requisites:
You should be familiar with using a
This article is written in vJass for use of
The Tutorial:
To begin, I'd like to open with an example script of an enumeration using a
Example A: Enumeration using a filter function
If you're newer to jass and you've never seen this before, take note that it was the standard practice for enumeration prior to the 1.24 wc3 update. With this method you could apply any number of conditions or actions to a group of units without creating, keeping track of, or destroying
However, there is another common method. We have a native called
Here is the equivalent function to the one above, but using a "first of group loop":
Example B: Enumeration using a first of group loop
That's all there is to it. You can now literally convert any filter function based enumeration to a first of group based one. Here's a few additional notes to keep in mind:
Additional notes
Advanced: Retaining group contents with a swap variable
What if you want to keep a group of units, and perform some actions on all the units without changing the group itself? We can cheat of course, by using a swap
Is this the only method? No. Indeed, for a long time, the standard practice was to:
What's wrong with this method? Nothing is strictly wrong with it -
Consider the following code which uses a swap group:
It would appear that this code is significantly slower than ForGroup() due to the overhead of adding units at each stage and swapping the handles - you'd be wrong. This method is faster because it doesn't start a new virtual thread of execution for each unit. In fact, the swapping method is 30% faster for 20 units, with non-diminishing returns at higher values.
I suspect that in due time, group utility libraries will be updated to accommodate this improvement, but for now you can script it yourself in an ad-hoc manner.
Preface:
This guide is intended for experienced jass users who have a goal of optimized triggers in their maps. My aim is to create a short, concise, and targeted tutorial that is easy to follow and navigate.
My primary audience is users who know how to use the best method of enumeration prior to the 1.24 warcraft 3 update - a
filterfunc that always return false'd. For these users, this tuturial will explain the "new" best way to do the same thing, and why you'll see this practice in code.The body of this article will be in example form, with only some minor explanation throughout.
Limitations:
The inherent idea of a First of Group loop is that the group is emptied each time it is used. This can be detrimental in the case that you want to save a group of units in a
group for use at different times and/or asynchronously.Pre-requisites:
You should be familiar with using a
filterfunc to run actions on groups of units, but this is not necessary to learn how a First of Group loop is done.This article is written in vJass for use of
globals blocks, which increases readabiliy. The same concepts are possible in vanilla JASS, but I recommend using JassHelper or just having JNGP to compile vJass.The Tutorial:
To begin, I'd like to open with an example script of an enumeration using a
filterfunc:Example A: Enumeration using a filter function
JASS:
scope filterfuncExample initializer i
globals
private group grp=CreateGroup() //We create the group on initialization, but never destroy it. The group never actually retains units, too, which means that you could potentially use one "tempGroup" for your whole map instead of one for your scope, as I do in this case.
endglobals
private function f takes nothing returns boolean
local unit fU=GetFilterUnit()
if GetUnitTypeId(fU)=='hfoo' then //this block is equivalent to imposing a condition and set of actions to enumerated units, but consolidated to one function.
call KillUnit(fU)
endif
set fU=null
return false //we return false so that our filter doesn't "pass" any unit. The group remains empty, but we apply our effects to a group of units anyway.
endfunction
private function i takes nothing returns nothing
call GroupEnumUnitsInRange(grp,0.,0.,256.,Filter(function f))
endfunction
endscopeIf you're newer to jass and you've never seen this before, take note that it was the standard practice for enumeration prior to the 1.24 wc3 update. With this method you could apply any number of conditions or actions to a group of units without creating, keeping track of, or destroying
groups.However, there is another common method. We have a native called
FirstOfGroup() which fetches the "first" unit of a group. It also happens to be a very fast native.Here is the equivalent function to the one above, but using a "first of group loop":
Example B: Enumeration using a first of group loop
JASS:
scope firstOfGroupLoopExample initializer i
globals
private group grp=CreateGroup()
endglobals
private function i takes nothing returns nothing
local unit FoG=null //We initially declare an empty unit handler
call GroupEnumUnitsInRange(grp,0.,0.,256.,null) //Note that we're using 'null' for our filterfunc. This means that *all* units in range will be added to the group.
loop
set FoG=FirstOfGroup(grp) //If you're new to this kind of loop, this part might look strange to you.
exitwhen FoG==null //combined with the above line, this is effectively checking if the group is empty
if GetUnitTypeId(FoG)=='hfoo' then //here we have a make-shift condition statement.. followed by an action below
call KillUnit(FoG)
endif
call GroupRemoveUnit(grp,FoG) //here's how we make the loop eventually terminate. Remove first of group, and when the loop restarts we get the new "first of group".
endloop
endfunction
endscopeThat's all there is to it. You can now literally convert any filter function based enumeration to a first of group based one. Here's a few additional notes to keep in mind:
Additional notes
- This method was also useable before 1.24, however the
nullincall GroupEnumUnitsInRange(grp,0.,0.,256.,null)caused an unavoidable leak. As a result you could still use first of group loops, but since a filterfunc was necessary to avoid the leak, first of group loops were actually slower. - This method also keeps the whole loop in-line, meaning that local variables don't need to unnecessarily be stored as globals as in the case with the
filterfuncmethod. - The reason this is faster (if you were wondering) is because
FirstOfGroup()is significantly faster than calling a filter function - even if you have to callFirstOfGroup()exponentially more often. - If you're asking yourself if all of this is actually necessary, the answer is "no, it's not", because the performance you'll save doing this, although large in relation, is actually so small that you shouldn't see a difference in any real application. The point of this is to encourage script structure that is uniform. As such, if you perform a
filterfuncenumeration in a system or spell which you submit to the hive, you will likely receive warning from more experienced scripters saying you should be using the first of group method.
Advanced: Retaining group contents with a swap variable
What if you want to keep a group of units, and perform some actions on all the units without changing the group itself? We can cheat of course, by using a swap
group and filling it in the scope of an FoG loop.Is this the only method? No. Indeed, for a long time, the standard practice was to:
- Enumerate units with a GroupEnumerate... native, potentially filtering them with a
filterfunc - Use the
ForGroup()native to perform actions on all the units and keep the group contents the same
What's wrong with this method? Nothing is strictly wrong with it -
ForGroup() is even still a useful method for cases when a new virtual thread of execution needs to be started.Consider the following code which uses a swap group:
JASS:
scope test
globals
private group iterator=CreateGroup()
private group swap=CreateGroup()
private group temp
endglobals
private function fgSwap takes nothing returns nothing
local unit FoG
loop
set FoG=FirstOfGroup(iterator)
exitwhen FoG==null
//
call GroupAddUnit(swap,FoG)
call GroupRemoveUnit(iterator,FoG)
endloop
set temp=iterator
set iterator=swap
set swap=temp
endfunction
endscopeIt would appear that this code is significantly slower than ForGroup() due to the overhead of adding units at each stage and swapping the handles - you'd be wrong. This method is faster because it doesn't start a new virtual thread of execution for each unit. In fact, the swapping method is 30% faster for 20 units, with non-diminishing returns at higher values.
I suspect that in due time, group utility libraries will be updated to accommodate this improvement, but for now you can script it yourself in an ad-hoc manner.
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