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Am 13.03.2014 13:43 schröbte David Crayford:

It's my mistake for sure. I copied the code from lua-cjson and the
finalizer gets called in that code in 5.1

I know it's something stupid but I don't know the C API well enough to
fix it. The full code is here

Your problem is that your finalizer method is pushed via `lua_pushcfunction` which doesn't include any upvalues, so you can't use your `fetch_config` function to access the userdata in `destroy_config`. The userdata is passed as first argument to the finalizer, so use

    ( ispf_config_t * )lua_touserdata( l, 1 );

instead. I'd recommend to prohibit access to your metatable, or use luaL_newmetatable and luaL_checkudata for additional type safety in your finalizer. There is also an `int` missing for `destroy_config`. The rest looks ok on first glance ...

On 12/03/2014 8:27 PM, Ignacio Burgueño wrote:
Unless I'm mistaken, that won't work with Lua 5.1 since the __gc
metamethod for tables was introduced in 5.2.
In this case, it does nothing. You'll need a userdata to achieve the
same effect.

The code (the one in the OP) already uses `__gc` on a userdata.

You should take a look at Thijs Schreijer's "Lua Library Template"

For instance, this example does what you want: