coding efficient vjass structs

Many people continue to ask me what the difference is between [lcode=jass]struct Hello[/lcode] and [lcode=jass]struct Hello extends array[/lcode] is.

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


struct a
endstruct


outputs


constant integer si__a=1
integer si__a_F=0
integer si__a_I=0
integer array si__a_V

//Generated allocator of a
function s__a__allocate takes nothing returns integer
local integer this=si__a_F //first node on recycle stack
    if (this!=0) then
        set si__a_F=si__a_V[this] //set stack to next node (like stack.next)
    else
        set si__a_I=si__a_I+1
        set this=si__a_I
    endif
    if (this>8190) then //protection against too many structs
        return 0
    endif

    set si__a_V[this]=-1 //set stack to -1 (stack.next = -1)
return this
endfunction

//Generated destructor of a
function s__a_deallocate takes integer this returns nothing
    if this==null then //don't deallocate null instance
        return
    elseif (si__a_V[this]!=-1) then //double free protection
        return
    endif
    set si__a_V[this]=si__a_F //set this.next = stack
    set si__a_F=this //set stack = this
endfunction



struct b extends a
endstruct


outputs


constant integer si__a=1
integer si__a_F=0
integer si__a_I=0
integer array si__a_V
constant integer si__b=2
integer array si__a_type
trigger array st__a_onDestroy //Trigger array?!?!
integer f__arg_this

//Generated allocator of a
function s__a__allocate takes nothing returns integer
local integer this=si__a_F
    if (this!=0) then
        set si__a_F=si__a_V[this]
    else
        set si__a_I=si__a_I+1
        set this=si__a_I
    endif
    if (this>8190) then
        return 0
    endif

    set si__a_type[this]=1
    set si__a_V[this]=-1
return this
endfunction

//Generated destructor of a
function sc__a_deallocate takes integer this returns nothing
    if this==null then
        return
    elseif (si__a_V[this]!=-1) then
        return
    endif
    set f__arg_this=this
    call TriggerEvaluate(st__a_onDestroy[si__a_type[this]]) //AHH!!
    set si__a_V[this]=si__a_F
    set si__a_F=this
endfunction

//Generated allocator of b
function s__b__allocate takes nothing returns integer
local integer this=s__a__allocate()
local integer kthis //why??
    if(this==0) then
        return 0
    endif
    set si__a_type[this]=2
    set kthis=this //... doesn't actually do anything

return this
endfunction


As can be seen, trigger evaluations pop up and useless variables get generated.


struct a extends array
endstruct


generates

[lcode=jass]constant integer si__a=1[/lcode]

Not bad, but this means that this sort of thing will no longer work

local a myStruct = a.create()
call myStruct.destroy()


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.

[lcode=jass]private static integer instanceCount = 0[/lcode]

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


private static thistype recycle = 0 //next recycled instance
private thistype recycleNext //recycled stack



struct MyStruct extends array
    private static integer instanceCount = 0
    private static thistype recycle = 0
    private thistype recycleNext

    static method create takes nothing returns thistype
        local thistype this

        //first check to see if there are any structs waiting to be recycled
        if (recycle == 0) then
            //if recycle is 0, there are no structs, so increase instance count
            set instanceCount = instanceCount + 1
            set this = instanceCount
        else
            //a struct is waiting to be recycled, so use it
            set this = recycle
            set recycle = recycle.recycleNext
        endif

        //perform creation code

        return this
    endmethod

    method destroy takes nothing returns nothing
        //add to recycle stack
        set recycleNext = recycle
        set recycle = this
    endmethod
endstruct


Code output from above (does same thing as first example w/o double free protection)


constant integer si__MyStruct=1
integer s__MyStruct_instanceCount= 0
integer s__MyStruct_recycle= 0
integer array s__MyStruct_recycleNext

function s__MyStruct_create takes nothing returns integer
    local integer this
    if ( s__MyStruct_recycle == 0 ) then
        set s__MyStruct_instanceCount=s__MyStruct_instanceCount + 1
        set this=s__MyStruct_instanceCount
    else
        set this=s__MyStruct_recycle
        set s__MyStruct_recycle=s__MyStruct_recycleNext[s__MyStruct_recycle]
    endif
    return this
endfunction

function s__MyStruct_destroy takes integer this returns nothing
    set s__MyStruct_recycleNext[this]=s__MyStruct_recycle
    set s__MyStruct_recycle=this
endfunction


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).


struct Mystruct2 extends array
    //delegate stores pointers to parent struct
    //this means that one can extend off of multiple structs
    private delegate MyStruct MyStruct
   
    static method create takes nothing returns thistype
        //base instance off of parent struct
        local thistype this = MyStruct.create()
        //store pointer into delegate
        set MyStruct = this
       
        return this
    endmethod
   
    method destroy takes nothing returns nothing
        //simply destroy
        call MyStruct.destroy()
    endmethod
endstruct


Outputs

constant integer si__MyStruct=1
integer s__MyStruct_instanceCount= 0
integer s__MyStruct_recycle= 0
integer array s__MyStruct_recycleNext
constant integer si__Mystruct2=2
integer array s__Mystruct2_MyStruct

function s__MyStruct_create takes nothing returns integer
local integer this
if ( s__MyStruct_recycle == 0 ) then
set s__MyStruct_instanceCount=s__MyStruct_instanceCount + 1
set this=s__MyStruct_instanceCount
else
set this=s__MyStruct_recycle
set s__MyStruct_recycle=s__MyStruct_recycleNext[s__MyStruct_recycle]
endif
return this
endfunction

function s__MyStruct_destroy takes integer this returns nothing
set s__MyStruct_recycleNext[this]=s__MyStruct_recycle
set s__MyStruct_recycle=this
endfunction

function s__Mystruct2_create takes nothing returns integer
local integer this= s__MyStruct_create()
set s__Mystruct2_MyStruct[this]=this
return this
endfunction

function s__Mystruct2_destroy takes integer this returns nothing
call s__MyStruct_destroy(s__Mystruct2_MyStruct[this])
endfunction


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

struct MyStruct extends array
    private static integer instanceCount = 0
    private static thistype recycle = 0
    private thistype recycleNext

    static method create takes nothing returns thistype
        local thistype this
        if (recycle == 0) then
            set instanceCount = instanceCount + 1
            set this = instanceCount
        else
            set this = recycle
            set recycle = recycle.recycleNext
        endif
        return this
    endmethod

    method destroy takes nothing returns nothing
        set recycleNext = recycle
        set recycle = this
    endmethod
endstruct

struct MyStruct2 extends array
    private static integer instanceCount = 0
    private static thistype recycle = 0
    private thistype recycleNext

    static method create takes nothing returns thistype
        local thistype this
        if (recycle == 0) then
            set instanceCount = instanceCount + 1
            set this = instanceCount
        else
            set this = recycle
            set recycle = recycle.recycleNext
        endif
        return this
    endmethod

    method destroy takes nothing returns nothing
        set recycleNext = recycle
        set recycle = this
    endmethod
endstruct

struct Mystruct3 extends array
    private delegate MyStruct MyStruct
    private delegate MyStruct2 MyStruct2
   
    static method create takes nothing returns thistype
        local thistype this = MyStruct.create()
        set MyStruct = this
       
        //use first pointer as current struct's instance
        set MyStruct2 = MyStruct2.create()
       
        //creation code
       
        return this
    endmethod
   
    method destroy takes nothing returns nothing
        //destroy both structs
        call MyStruct.destroy()
        call MyStruct2.destroy()
    endmethod
endstruct


Which happily outputs

constant integer si__MyStruct=1
integer s__MyStruct_instanceCount= 0
integer s__MyStruct_recycle= 0
integer array s__MyStruct_recycleNext
constant integer si__MyStruct2=2
integer s__MyStruct2_instanceCount= 0
integer s__MyStruct2_recycle= 0
integer array s__MyStruct2_recycleNext
constant integer si__Mystruct3=3
integer array s__Mystruct3_MyStruct
integer array s__Mystruct3_MyStruct2

function s__MyStruct_create takes nothing returns integer
local integer this
if ( s__MyStruct_recycle == 0 ) then
set s__MyStruct_instanceCount=s__MyStruct_instanceCount + 1
set this=s__MyStruct_instanceCount
else
set this=s__MyStruct_recycle
set s__MyStruct_recycle=s__MyStruct_recycleNext[s__MyStruct_recycle]
endif
return this
endfunction

function s__MyStruct_destroy takes integer this returns nothing
set s__MyStruct_recycleNext[this]=s__MyStruct_recycle
set s__MyStruct_recycle=this
endfunction


function s__MyStruct2_create takes nothing returns integer
local integer this
if ( s__MyStruct2_recycle == 0 ) then
set s__MyStruct2_instanceCount=s__MyStruct2_instanceCount + 1
set this=s__MyStruct2_instanceCount
else
set this=s__MyStruct2_recycle
set s__MyStruct2_recycle=s__MyStruct2_recycleNext[s__MyStruct2_recycle]
endif
return this
endfunction

function s__MyStruct2_destroy takes integer this returns nothing
set s__MyStruct2_recycleNext[this]=s__MyStruct2_recycle
set s__MyStruct2_recycle=this
endfunction


function s__Mystruct3_create takes nothing returns integer
local integer this= s__MyStruct_create()
set s__Mystruct3_MyStruct[this]=this
set s__Mystruct3_MyStruct2[this]=s__MyStruct2_create()
return this
endfunction

function s__Mystruct3_destroy takes integer this returns nothing
call s__MyStruct_destroy(s__Mystruct3_MyStruct[this])
call s__MyStruct2_destroy(s__Mystruct3_MyStruct2[this])
endfunction