coding efficient vjass structs

Jass Tutorials

14 years
edited 8 years
Many people continue to ask me what the difference is between struct Hello and struct Hello extends array is.

In vJASS, regular structs create some extra code in the background to make themselves work.

Code (jass) Select
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struct a
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endstruct
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outputs

	
Code (jass) Select 
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constant integer si__a=1
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integer si__a_F=0
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integer si__a_I=0
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integer array si__a_V
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//Generated allocator of a
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function s__a__allocate takes nothing returns integer
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 local integer this=si__a_F //first node on recycle stack
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    if (this!=0) then
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        set si__a_F=si__a_V[this] //set stack to next node (like stack.next)
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    else
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        set si__a_I=si__a_I+1
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        set this=si__a_I
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    endif
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    if (this>8190) then //protection against too many structs
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        return 0
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    endif
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    set si__a_V[this]=-1 //set stack to -1 (stack.next = -1)
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 return this
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endfunction
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//Generated destructor of a
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function s__a_deallocate takes integer this returns nothing
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    if this==null then //don't deallocate null instance
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        return
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    elseif (si__a_V[this]!=-1) then //double free protection
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        return
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    endif
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    set si__a_V[this]=si__a_F //set this.next = stack
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    set si__a_F=this //set stack = this
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endfunction
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Code (jass) Select 
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struct b extends a
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endstruct
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outputs

	
Code (jass) Select 
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constant integer si__a=1
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integer si__a_F=0
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integer si__a_I=0
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integer array si__a_V
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constant integer si__b=2
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integer array si__a_type
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trigger array st__a_onDestroy //Trigger array?!?!
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integer f__arg_this
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//Generated allocator of a
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function s__a__allocate takes nothing returns integer
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 local integer this=si__a_F
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    if (this!=0) then
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        set si__a_F=si__a_V[this]
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    else
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        set si__a_I=si__a_I+1
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        set this=si__a_I
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    endif
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    if (this>8190) then
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        return 0
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    endif
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    set si__a_type[this]=1
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    set si__a_V[this]=-1
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 return this
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endfunction
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//Generated destructor of a
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function sc__a_deallocate takes integer this returns nothing
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    if this==null then
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        return
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    elseif (si__a_V[this]!=-1) then
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        return
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    endif
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    set f__arg_this=this
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    call TriggerEvaluate(st__a_onDestroy[si__a_type[this]]) //AHH!!
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    set si__a_V[this]=si__a_F
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    set si__a_F=this
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endfunction
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//Generated allocator of b
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function s__b__allocate takes nothing returns integer
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 local integer this=s__a__allocate()
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 local integer kthis //why??
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    if(this==0) then
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        return 0
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    endif
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    set si__a_type[this]=2
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    set kthis=this //... doesn't actually do anything
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 return this
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endfunction
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As can be seen, trigger evaluations pop up and useless variables get generated. 

	
Code (jass) Select 
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struct a extends array
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endstruct
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generates

constant integer si__a=1

Not bad, but this means that this sort of thing will no longer work
	
Code (jass) Select 
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local a myStruct = a.create()
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call myStruct.destroy()
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meaning that the allocation and deallocation of structs is left up to the coders.

So let's look on how structs are actually allocated (getting rid of the virtually useless double free protection and getting rid of allocate/deallocate as they might as well be put into create and destroy).

As structs are created, the total number of structs generated continues to increase. A counter is needed in order to track how many structs have been created.

private static integer instanceCount = 0

As structs are destroyed, their instances need to be recycled.

	
Code (jass) Select 
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private static thistype recycle = 0 //next recycled instance
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private thistype recycleNext //recycled stack
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Code (jass) Select 
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struct MyStruct extends array
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    private static integer instanceCount = 0
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    private static thistype recycle = 0
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    private thistype recycleNext
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    static method create takes nothing returns thistype
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        local thistype this
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        //first check to see if there are any structs waiting to be recycled
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        if (recycle == 0) then
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            //if recycle is 0, there are no structs, so increase instance count
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            set instanceCount = instanceCount + 1
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            set this = instanceCount
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        else
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            //a struct is waiting to be recycled, so use it
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            set this = recycle
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            set recycle = recycle.recycleNext
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        endif
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        //perform creation code
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        return this
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    endmethod
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    method destroy takes nothing returns nothing
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        //add to recycle stack
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        set recycleNext = recycle
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        set recycle = this
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    endmethod
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endstruct
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Code output from above (does same thing as first example w/o double free protection)

	
Code (jass) Select 
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constant integer si__MyStruct=1
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integer s__MyStruct_instanceCount= 0
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integer s__MyStruct_recycle= 0
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integer array s__MyStruct_recycleNext
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function s__MyStruct_create takes nothing returns integer
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    local integer this
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    if ( s__MyStruct_recycle == 0 ) then
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        set s__MyStruct_instanceCount=s__MyStruct_instanceCount + 1
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        set this=s__MyStruct_instanceCount
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    else
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        set this=s__MyStruct_recycle
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        set s__MyStruct_recycle=s__MyStruct_recycleNext[s__MyStruct_recycle]
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    endif
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    return this
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endfunction
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function s__MyStruct_destroy takes integer this returns nothing
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    set s__MyStruct_recycleNext[this]=s__MyStruct_recycle
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    set s__MyStruct_recycle=this
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endfunction
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A bit more work, but a bit more optimal. What about extending structs?

Extending structs is done with delegates (also allows members to be overriden).

	
Code (jass) Select 
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struct Mystruct2 extends array
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    //delegate stores pointers to parent struct
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    //this means that one can extend off of multiple structs
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    private delegate MyStruct MyStruct
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    static method create takes nothing returns thistype
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        //base instance off of parent struct
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        local thistype this = MyStruct.create()
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        //store pointer into delegate
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        set MyStruct = this
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        return this
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    endmethod
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    method destroy takes nothing returns nothing
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        //simply destroy
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        call MyStruct.destroy()
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    endmethod
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endstruct
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Outputs
	
Code (jass) Select 
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constant integer si__MyStruct=1
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integer s__MyStruct_instanceCount= 0
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integer s__MyStruct_recycle= 0
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integer array s__MyStruct_recycleNext
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constant integer si__Mystruct2=2
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integer array s__Mystruct2_MyStruct
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function s__MyStruct_create takes nothing returns integer
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	local integer this
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	if ( s__MyStruct_recycle == 0 ) then
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		set s__MyStruct_instanceCount=s__MyStruct_instanceCount + 1
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		set this=s__MyStruct_instanceCount
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	else
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		set this=s__MyStruct_recycle
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		set s__MyStruct_recycle=s__MyStruct_recycleNext[s__MyStruct_recycle]
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	endif
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	return this
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endfunction
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function s__MyStruct_destroy takes integer this returns nothing
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	set s__MyStruct_recycleNext[this]=s__MyStruct_recycle
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	set s__MyStruct_recycle=this
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endfunction
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function s__Mystruct2_create takes nothing returns integer
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	local integer this= s__MyStruct_create()
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	set s__Mystruct2_MyStruct[this]=this
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	return this
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endfunction
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function s__Mystruct2_destroy takes integer this returns nothing
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	call s__MyStruct_destroy(s__Mystruct2_MyStruct[this])
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endfunction
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No trigger arrays, no trigger evaluations, and no wasted local variables. It even allows you to make one struct extend off of multiple structs.

Multi-Struct Extension
	
Code (jass) Select 
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struct MyStruct extends array
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    private static integer instanceCount = 0
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    private static thistype recycle = 0
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    private thistype recycleNext
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    static method create takes nothing returns thistype
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        local thistype this
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        if (recycle == 0) then
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            set instanceCount = instanceCount + 1
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            set this = instanceCount
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        else
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            set this = recycle
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            set recycle = recycle.recycleNext
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        endif
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        return this
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    endmethod
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    method destroy takes nothing returns nothing
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        set recycleNext = recycle
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        set recycle = this
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    endmethod
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endstruct
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struct MyStruct2 extends array
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    private static integer instanceCount = 0
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    private static thistype recycle = 0
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    private thistype recycleNext
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    static method create takes nothing returns thistype
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        local thistype this
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        if (recycle == 0) then
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            set instanceCount = instanceCount + 1
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            set this = instanceCount
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        else
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            set this = recycle
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            set recycle = recycle.recycleNext
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        endif
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        return this
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    endmethod
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    method destroy takes nothing returns nothing
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        set recycleNext = recycle
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        set recycle = this
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    endmethod
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endstruct
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struct Mystruct3 extends array
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    private delegate MyStruct MyStruct
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    private delegate MyStruct2 MyStruct2
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    static method create takes nothing returns thistype
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        local thistype this = MyStruct.create()
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        set MyStruct = this
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        //use first pointer as current struct's instance
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        set MyStruct2 = MyStruct2.create()
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        //creation code
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        return this
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    endmethod
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    method destroy takes nothing returns nothing
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        //destroy both structs
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        call MyStruct.destroy()
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        call MyStruct2.destroy()
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    endmethod
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endstruct
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Which happily outputs
	
Code (jass) Select 
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constant integer si__MyStruct=1
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integer s__MyStruct_instanceCount= 0
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integer s__MyStruct_recycle= 0
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integer array s__MyStruct_recycleNext
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constant integer si__MyStruct2=2
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integer s__MyStruct2_instanceCount= 0
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integer s__MyStruct2_recycle= 0
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integer array s__MyStruct2_recycleNext
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constant integer si__Mystruct3=3
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integer array s__Mystruct3_MyStruct
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integer array s__Mystruct3_MyStruct2
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function s__MyStruct_create takes nothing returns integer
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	local integer this
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	if ( s__MyStruct_recycle == 0 ) then
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		set s__MyStruct_instanceCount=s__MyStruct_instanceCount + 1
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		set this=s__MyStruct_instanceCount
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	else
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		set this=s__MyStruct_recycle
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		set s__MyStruct_recycle=s__MyStruct_recycleNext[s__MyStruct_recycle]
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	endif
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	return this
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endfunction
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function s__MyStruct_destroy takes integer this returns nothing
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	set s__MyStruct_recycleNext[this]=s__MyStruct_recycle
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	set s__MyStruct_recycle=this
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endfunction
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function s__MyStruct2_create takes nothing returns integer
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	local integer this
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	if ( s__MyStruct2_recycle == 0 ) then
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		set s__MyStruct2_instanceCount=s__MyStruct2_instanceCount + 1
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		set this=s__MyStruct2_instanceCount
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	else
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		set this=s__MyStruct2_recycle
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		set s__MyStruct2_recycle=s__MyStruct2_recycleNext[s__MyStruct2_recycle]
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	endif
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	return this
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endfunction
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function s__MyStruct2_destroy takes integer this returns nothing
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	set s__MyStruct2_recycleNext[this]=s__MyStruct2_recycle
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	set s__MyStruct2_recycle=this
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endfunction
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function s__Mystruct3_create takes nothing returns integer
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	local integer this= s__MyStruct_create()
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	set s__Mystruct3_MyStruct[this]=this
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	set s__Mystruct3_MyStruct2[this]=s__MyStruct2_create()
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	return this
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endfunction
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function s__Mystruct3_destroy takes integer this returns nothing
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	call s__MyStruct_destroy(s__Mystruct3_MyStruct[this])
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	call s__MyStruct2_destroy(s__Mystruct3_MyStruct2[this])
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endfunction
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