Re: Confusion about environments in Lua 5.2

[Philipp Janda <siffiejoe@...>]

Am 09.04.2014 06:13 schröbte Milind Gupta:
> I did the following:
>
> > print(_G)
> table: 00C31B98
> > print(_ENV)
> table: 00C31B98
> > print(_G._G)
> table: 00C31B98
> > print(_ENV._G)
> table: 00C31B98
> > print(_ENV._ENV)
> nil
> > print(_G._ENV)
> nil

`_ENV` is an upvalue not a global. So it isn't in the globals table 
referenced by `_ENV` or `_G` (which really is `_ENV._G`).

> when I do print(_ENV) doesn't it access the variable _ENV._ENV? but
> printing _ENV._ENV is nil. So does it mean when I access any other variable
> aexcept _ENV it is accessed as _ENV.var?

No. The rule is simple. When you access a variable `x` you get the 
innermost local or upvalue with that name in scope, or as a last resort 
the global variable `_ENV.x` if there is none in scope.

>    So this means that a running code cannot change its own environment as it
> could do in Lua 5.1.

Sure it can:

    _ENV = {}

> Milind

Philipp