Re: Basic question on weak keys

[Rena <hyperhacker@...>]

On Wed, Jun 13, 2012 at 8:12 PM, TNHarris <telliamed@whoopdedo.org> wrote:
> On Wednesday, June 13, 2012 05:59:54 PM Andrew Starks wrote:
>>
>> Why nil? I thought that since a[b] was not weak, it would keep it as a
>> reference? What does __mode ="k" do if an object is collected  when it
>> is used in a table as a key? Can someone be so kind as to provide an
>> example?
>>
>
> As has been mentioned, you are not testing what you think you're testing.
> Consider this instead.
>
>    a = {}
>    b = {}
>    a[b] = "foo"
>    for k,v in pairs(a) do print(k,v) end
>    --> table: 0x18066a0        foo
>    b = nil
>    collectgarbage('collect')
>    for k,v in pairs(a) do print(k,v) end
>    --> table: 0x18066a0        foo
>
> In contrast,
>
>    a = setmetatable({}, {__mode="k"})
>    b = {}
>    a[b] = "foo"
>    for k,v in pairs(a) do print(k,v) end
>    --> table: 0xd9f8b0         foo
>    b = nil
>    collectgarbage('collect')
>    for k,v in pairs(a) do print(k,v) end
>    -->
>
>
> -----
> -- tom
> telliamed@whoopdedo.org
>

...but note that the behaviour of the garbage collector isn't
guaranteed, and can be tweaked, so b might not be collected after one
cycle. Or so I've heard...

-- 
Sent from my Game Boy.