Discussion A way to detect if an handle is invalid

[Troll-Brain]

Maybe most of you already know but you can't store a "null" handle in an hashtable, neither an invalid handle, for example an handle which was destroyed but not setted to null.

I've just realized recently we can use that for safety checks.

library CheckHandles initializer onInit

globals
    private hashtable HashT
endglobals

function IsGroupValid takes group whichGroup returns boolean
    return SaveGroupHandle(HashT,0,0,whichGroup)
endfunction

private function onInit takes nothing returns nothing
    set HashT = InitHashtable()
endfunction

endlibrary

Note that i'm perfectly aware about the priority of module initializer.
And yes, i could initialize the hashtable in the global declaration.
And ofc it might have better ways for specifics handles, like for units (GetUnitTypeId(<unit>) != 0)

What you think about that ?
A such library may exist ?

If it's really obvious, then amen, at least it wasn't for me

 

[kingkingyyk3]

function IsHandleValid takes handle h returns boolean
    return GetHandleId(h) != 0
endfunction

Try?

 

[Troll-Brain]

function IsHandleValid takes handle h returns boolean
    return GetHandleId(h) != 0
endfunction

Try?

That was a nice idea but it doesn't work, it displays "true".

library CheckHandles initializer onInit

globals
    private hashtable HashT
endglobals

function IsGroupValid takes group whichGroup returns boolean
    return SaveGroupHandle(HashT,0,0,whichGroup)
endfunction

function IsHandleValid takes handle h returns boolean
    return GetHandleId(h) != 0
endfunction

private function onInit takes nothing returns nothing
    local group g = CreateGroup()
    call DestroyGroup(g)
    set HashT = InitHashtable()
    call TriggerSleepAction(1.)
    if IsHandleValid(g) then
        call BJDebugMsg("true")
    else
        call BJDebugMsg("false")
    endif
    
endfunction

endlibrary

Probably because the id isn't recycled (g isn't null), it returns a valid integer.

EDIT :

This works properly :

function IsAgentValid takes agent whichAgent returns boolean
    return SaveAgentHandle(HashT,0,0,whichAgent)
endfunction

But i would a prefer a specific function for each type though.

 

[Jesus4Lyf]

What purpose would this serve?

 

[Troll-Brain]

What purpose would this serve?

I usually add this kind of check when a function/method use an argument, i don't believe in humans or even myself, but before i simply checked for null.

 

[Darthfett]

What purpose would this serve?

globals
    integer i = 0
endglobals

function DoSomethingCallback takes nothing returns nothing
    set i = i + 1
endfunction

function DoSomething takes group g returns integer
    set i = 0
    //if g != null then
    if IsAgentValid(g) then
        call ForGroup(g,function DoSomethingCallback)
        return 5 / i //without IsAgentValid, this will divide by 0.
    endif
    return 5
endfunction

function Test takes nothing returns nothing
    local group g = CreateGroup()
    call DestroyGroup(g)
    call DoSomething(g) //Oops!  Someone passed a non-null, but non-existant group!
endfunction

 

[Troll-Brain]

It returns false if the agent is null or is a ghost one like in my example showed before or your's, and true only if he is valid.

 

[Lyerae]

function IsHandleValid takes handle h returns boolean
    return GetHandleId(h) != 0
endfunction

Try?

function isHandleValid takes handle whichHandle returns boolean // you guys should use more descriptive arguement names. Even in examples. :/
     return whichHandle != null
endfunction

?

 

[kingkingyyk3]

function isHandleValid takes handle whichHandle returns boolean // you guys should use more descriptive arguement names. Even in examples. :/
     return whichHandle != null
endfunction

?

A variable with destroyed group does not have the value of null.

 

[Troll-Brain]

Exactly, without benchmark it's pretty obvious that IsAgentValid is lightning fast, probably only 2 time slower than a variable setting.
I already use it instead of comparing to null (if i don't already need to store the argument in an hashtable ofc).

@Lyerae : So what, should i add the comment, "return true if handle is valid, and false if it is not", seems really obvious

 

[Lyerae]

No, but [ljass]integer index[/ljass] is better than [ljass]integer i[/ljass] (as an example).

 

[Troll-Brain]

No, but [ljass]integer index[/ljass] is better than [ljass]integer i[/ljass] (as an example).

Stop whining really.

I assume you wanted to say that since long time ago, but here it's pretty pointless, choice an other thread

Back on topic, i see that's not obvious so, at least for all persons which have posted here, i will make a such library then.
But in an other hand, it should be used for personal codes only, since it's easy to inline it, hmm maybe as a sample ?

 

[Lyerae]

Stop whining really.

Now whining, just commenting.

I assume you wanted to say that since long time ago/

Not really.

 

[Darthfett]

No, but [ljass]integer index[/ljass] is better than [ljass]integer i[/ljass] (as an example).

Seriously? :nuts:

'i' is a standard name known to be used for an index, or iterator. Just the name of the function is enough to know what it's going to take and what it's going to do.

The code is not complicated, and sometimes simple code is the best.

 

[Troll-Brain]

I just want to say that in Darthfett's example, it will divide by 0 also if the group is empty or at least full of ghost units only.