Global variables?
Well, of course there is no such thing. The manuall tells us so.
"The Lua library is fully reentrant: it has no global variables."
That's referring to C globals within the C code.
And as we all know, what looks like a global variable 'var' in a Lua
5.2 or 5.3 script is just syntactic sugar for '_ENV.var'.
The API nevertheless talks like there are global variables:
int lua_getglobal (lua_State *L, const char *name);
Pushes onto the stack the value of the global 'name'. Returns the
type of that value.
Are these globals the same thing as global variables in a Lua script?
Of course. The Lua language has plenty of global variables. It's just the C code that implements Lua that doesn't.
Let's see. These refer to table entries in "the global environment
stored at index LUA_RIDX_GLOBALS in the registry". (RIDX means
registry index).
So they are the same if and only tf "the global environment" is the
same as _ENV. This is the case when you start up Lua, but if you
fiddle around with _ENV, it does not mean that "the global
environment" is different too, only that you can no longer see it
(unless of course you were prudent enough to have stored _G in a local
variable).
So is 'lua_getglobal' exposed at the Lua level? In other words, is
there anything you can do to retrieve an original global variable if
_ENV has changed? Obviously you can if you copied over either _G or
the debug library. Any other way?
This is an interesting question, though.
