Emptying a Table

[kerrang]

Here's a challenge for you

Fred = {}
Fred['barney'] = {}
Fred['barney']['wilma'] = "Flintstone"
Fred = nil
Fred = {}
Fred['barney'] = {}

What does Fred['barney']['wilma'] now contain

Clue: It's not nil, "" nor does it not exist

How does one actually empty a table then?

[Slakah]

Originally Posted by kerrang Here's a challenge for you Fred = {} Fred['barney'] = {} Fred['barney']['wilma'] = "Flintstone" Fred = nil Fred = {} Fred['barney'] = {} What does Fred['barney']['wilma'] now contain Clue: It's not nil, "" nor does it not exist How does one actually empty a table then?

Fred = {}
Fred['barney'] = {}
print(Fred['barney'])
Fred['barney']['wilma'] = "Flintstone"
Fred = nil
Fred = {}
Fred['barney'] = {}
print(Fred['barney'])
print(Fred['barney']['wilma'])

outputs

table: 0036B180
table: 0036B290
nil

[LBXZero]

I believe it should be nil unless you have a local variable in a block using the same name. Then for that block it will fool you.

If Fred is a global, you can also setglobal("Fred",nil).

[kerrang]

In my case, Fred is declared at the highest level within my addon - it's actually a 'savedvariable' too.

After

Fred = {}
Fred['barney'] = {}
print(Fred['barney'])
Fred['barney']['wilma'] = "Flintstone"
Fred = nil
Fred = {}
Fred['barney'] = {}
print(Fred['barney']['wilma'])

results in "Flintstone"

I've actually changed

Fred = nil

to

for val = pairs(Fred) do
for val2 in pairs(Fred[val]) do
Fred[val][val2] = nil
end
end
Fred = nil

and that resets it...

Something related to the way SavedVariables work perhaps?

[kerrang]

I've come across a second instance where emptying a table isn't actually emptying it - in that recreating a key which existed before will bring back values previous held for that key...

This time it's not a savedvariable but it is defined at the highest level of the addon's scope.

I can only assume this is a bug in the Blizzard lua implementation?

The statement

mytable = {}

SHOULD clear EVERYTHING in the existing table should it not?

[LBXZero]

If I understand what you are saying, try this for cleaning the table. Create a dummy variable with a new blank table and set your global variable to that blank table.

local blanktable = {};
setglobal("fred",blanktable);

I am just thinking this up, so I really have not tried it nor can immediately comfirm if it will run.

[arkayenro]

Originally Posted by kerrang mytable = {} SHOULD clear EVERYTHING in the existing table should it not?

clear the table? no. youre assigning a new empty table to that variable and throwing the old one onto the lua garbage heap, it still exists in memory but it shouldnt be allocated to your variable any more.

how it's getting reassigned to your variable is weird, but its got to be in your code somewhere.

are you using any savedvaraible libraries? like acedb or similar? or is this from no library code?

[Iriel]

Your problem is almost certainly that you're doing all those operations BEFORE the saved variables are loaded, and the game then simply restores the old value of the table.

[kerrang]

It's nothing to do with savedvariables - I've seen a similar issue in 2 addons and the table is only a 'savedvariable' in one of those addons so...

It's not behaviour before VARIABLES_LOADED either - this is something you can see after you've been playing for HOURS

Furthermore - 2 users have reported bugs which could ONLY be caused by a table not being completely emptied - so it's not just me The addon in question resets it's table VERY often - and yet we see 'weirdness' which goes away after a "/console reloadui" and the ONLY thing that would do is 'properly' clear the tables.

I think the issue is with tables WITHIN tables - and it may be down to my ignorance of how this should work of course.

It's not an easy bug to reproduce - there seems to be a specific set of circumstances (most likely related to being in/out of combat) but what I seem to be seeing is

fred['a'] = {}
fred ['a']['a'] = 1
fred ['a']['b'] = 1
fred ['a']['c'] = 1
fred = {}
fred['a'] = {}
fred ['a']['a'] = 1

At this point fred ['a']['b'] == 1

If, instead of using fred = {} I do something like

for v in pairs(fred) do
fred[v] = {}
end

I never see the issue - so that's what my addons do to clear tables right now. If I ever went to a 3rd level of 'nesting' I guess I'd have to reset both levels - and so on...

[kerrang]

Originally Posted by arkayenro are you using any savedvaraible libraries? like acedb or similar? or is this from no library code?

No libraries whatsoever...

[Duugu]

imho this is about weak tables and/or the garbage collection.

Please read http://www.lua.org/pil/17.html and http://www.lua.org/manual/5.1/manual.html#2.10.

[edit]
Could you please state which mod we're talking about?