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- Subject: Re: How to change _ENV's value in a pure C function?
- From: While Loop <towlyhk-luageneral@...>
- Date: Thu, 29 Dec 2011 11:25:39 +0800 (SGT)
Xavier Wang <weasley.wx <at> gmail.com> writes:
> I'm wonder how to change _ENV's value, or rebuild a new _ENV locals in
> C function. the only idea I make out is using a wrapping lua code:
> lua_pushcfunction(L, myfunc);
> luaL_loadstring(L, "local _ENV,func = ... return func()");
> lua_call(L, 2, 0);
> Is there any other method to change _ENV in a C function using a pure C API?
I have no experience in writing C module. But I try to sum up a few points
from the Lua 5.2 manual. If I am wrong someone please correct me.
(1) C function no longer have environment.
LUA_ENVIRONINDEX and lua_getfenv are removed.
(2) There is no _ENV for the C function itself. There is no way to change
_ENV variable of the caller lua function. You can only change things
inside the associated table.
(3) C function do no inherit environment (and value/vars) from Lua function.
To access value/vars in the environment of the caller lua function,
pass the _ENV table or other variables to the C function as augement.
(4) If the C function return a new function and you want to enclose some
values/vars in _ENV of the caller lua function to the new function.
You have to make a copy of those values/vars and associate them with
the new function by lua_pushcclosure or lua_setupvalue.
But the description of lua_getupvalue/lua_setupvalue is not very clear.
lua_getupvalue [-0, +(0|1), –]
const char *lua_getupvalue (lua_State *L, int funcindex, int n);
... (Upvalues have no particular order, as they are active through the
whole function. So, they are numbered in an arbitrary order.)
... For C functions, this function uses the empty string "" as a name for all upvalues.
Upvalues have no name, and lua_getupvalue return them in arbitrary order !!??
How to distinguish which value is which value ??