Re: [Lua5.4] lua_toclose will close the wrong value
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- Subject: Re: [Lua5.4] lua_toclose will close the wrong value
- From: Sean Conner <sean@...>
- Date: 2019年5月21日 13:52:33 -0400
It was thus said that the Great actboy168 once stated:
> #include <lua.h>
> #include <lauxlib.h>
>
> static int close(lua_State *L) {
> return 0;
> }
>
> static void newtable(lua_State *L) {
> static const luaL_Reg mt[] = {
> {"__close", close},
> {NULL, NULL}
> };
> lua_newtable(L);
> luaL_newlib(L, mt);
> lua_setmetatable(L, -2);
> }
>
> int luaopen_toclose(lua_State *L) {
> lua_pushinteger(L, 1);
> newtable(L);
> lua_toclose(L, -1);
> lua_remove(L, -2); // throw error: attempt to close non-closable variable '?'
> return 1;
> }
Okay, I removed the call to lua_remove() and that cleared up the error
message. I then added a call to printf() in the close() function and did
the the following Lua code:
do
local x = require "toclose"
print(x)
end
The output I got was:
CLOSING!
table: 0x949aa70
Going back to the manual:
Here, in the context of a C function, to go out of scope means that
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
the running function returns to Lua, there is an error, or the index
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
is removed from the stack through lua_settop or lua_pop. An index
marked as to-be-closed should not be removed from the stack by any
other function in the API except lua_settop or lua_pop.
(emphasis added)
So that explains "CLOSING" being printed before variable x being printed.
It also seems that once a variable is marked "toclose" on the stack in C,
then one should not shift it about via lua_remove() (and possibly
lua_insert()). It's looking like the manual should clarify aspects of
toclose variables on the C side of things.
-spc