RE: metatable and c++ assistance/thoughts

["Kevin Baca" <lualist@...>]

The only way to receive a __gc event on a user data is to make it a full
user data with a metatable that contains a __gc metamethod.

A relatively lightweight way to do this is to use Lua's "boxpointer" set
of macros.

<code>
    lua_boxpointer( L, my_pointer);
    lua_newtable( L );
    lua_pushstring( L, "__gc" );
    lua_pushcfunction( L, myGCFunction );
    lua_settable( L, -3 );
    lua_setmetatable( L, -2 );
</code>

<code>
int myGCFunction( lua_State* L )
{
    MyData* my_pointer = ( MyData* ) lua_unboxpointer( L, 1 )

    delete my_pointer;
}
</code>

-Kevin

> -----Original Message-----
> From: lua-bounces@bazar2.conectiva.com.br 
> [mailto:lua-bounces@bazar2.conectiva.com.br] On Behalf Of 
> Robert Sadedin
> Sent: Monday, October 18, 2004 7:53 PM
> To: lua@bazar2.conectiva.com.br
> Subject: metatable and c++ assistance/thoughts
> 
> 
> Hi all,
> 
> I'm trying to work with objects in both lua and c++, and am 
> playing with 
> creating a table from c++ with static methods from c++ linked 
> into table 
> functions, and a pointer to the c++ object stored in the 
> table with some 
> appropriate name (this, for instance).
> Then, when a table method is called with the : operator, the table is 
> passed,  I can extract the pointer, and everything is groovy 
> then to call 
> the object from c++.
> 
> I want to control the garbage collection on the object, 
> though, since at 
> present it leaks terribly because the garbage collector 
> doesn't fire on the 
> lightuserdata I'm storing the pointer as.
> 
> I can make it a userdata, and specifically create it and add 
> a metatable to 
> it for __gc, but I'd rather not have to.
> 
> Is there anyway I can control destruction of a table (appears 
> not from the 
> manual)?  Perhaps people can very quickly say I'm simply a 
> fool for thinking 
> of managing things in the manner I've set out ... ?
> 
> 
> 
> Rob
>