Re: 5.2 _ENV garbage collection question

[Jerome Vuarand <jerome.vuarand@...>]

2011/6/27 Gaspard Bucher <gaspard@teti.ch>:
> Hi list !
> I am experimenting with the _ENV value. From my understanding, _ENV = xxx is
> now a special lua construct:
> 1. normal construct
> name = 'xxx'  --- _ENV.name = 'xxx'
> 2. special _ENV construct
> _ENV = {}   --- replace _ENV in place
> My question is: since the new _ENV is not assigned to any preexisting
> environment (it is not _ENV._ENV), is it correct to say that it is assigned
> to the chunk's environment, replacing the previous value ? But then I would
> expect values in the previous _ENV to be garbage collected but they are not.
> Any hint ?
> =============================== test.lua (5.2)
> local print = print
> local collectgarbage = collectgarbage
> local gc_mt = {}
> function gc_mt.__gc(obj)
>   print('gc', obj.name)
> end
> foo = {name = 'foo'}
> setmetatable(foo, gc_mt)
> _ENV = {}
> print(foo)     ---- nil as expected
> collectgarbage() ---- does not collect old "foo". Why ? Where is it stored ?
> print('end') -- the garbage collection after 'end' removes old "foo".
> ===============================

I think you may need to call collectgarbage twice for the finalizer to
be called.