Re: doubt about gc

[Diego Fernandes Nehab <diego@...>]

Hi,

> I would like to know if when I execute the code shown below, the garbage
> collector can "clean" the lost data.

x = {}
y = {}
x[y] = 1 -- lost data
y = nil

> I ask this because I am using this type of indexation to put into Private
> table private attributes concerning an object, and when this object is
> destructed I want that your private data also be destructed.

With  normal tables,  keys are  considered by  the garbage  collector as
references to their values. Therefore, it doesn't matter whether you set
'y' to  nil. The value  will stil  be referenced by  the key and  the GC
won't be able to collect either the key or associated data.

Lua 4.1  introduced weak keys. When  traversing a table with  weak keys,
the garbage  collector ignores  its keys  when checking  for references.
Therefore, since you set  y to nil, there will be  no references to that
old value and it will be collected. Once it is collected, the associated
data can also be collected.

So, yes, you can do that with Lua  4.1. I had never seen any utility for
this,  and I  am  glad  you showed  me  one. Hope  it  works  the way  I
described. :-)

Regards,
Diego.