Cannot reimplement luaL_tolstring / No accessible way for lua_topointer about rlua HOT 4 CLOSED

Could this be solved by borrowing the value (which requires knowing its type, which shouldn't be a big hurdle for us) and then getting a pointer to the inner value?

e.g:

let ref = user_data.borrow::<Tag>()?;
println!("Pointer is {:p}", &*ref as *const Tag);

from rlua.

Uhm... now I wonder what the problem was that made me conclude that the above does not work. However, I have no idea what that was....O.o
(Perhaps I got confused by the get_object() function in way-cooler since that clones the object...)

Sorry for the noise!

from rlua.

I'm glad you got it figured out! I didn't know about __name before, and apparently it's used by some error reporting functions as well? I might look into allowing that to be set on userdata metatables, but like everything else on userdata metatables it would probably be the same for all instances of a UserData.

from rlua.

Could this be solved by borrowing the value (which requires knowing its type, which shouldn't be a big hurdle for us) and then getting a pointer to the inner value?

The short version: Yes, but I forgot to do a dereference (*) when testing. You apparently did not forget this. :-)

Okay, I finally had the time to actually try this and... it does not work.

extern crate rlua;

use rlua::{Lua, AnyUserData, UserData, Result};

struct MyData();

impl UserData for MyData {}

fn run() -> Result<()> {
    let lua = Lua::new();
    lua.globals().set("object", MyData())?;

    let value = lua.globals().get::<_, AnyUserData>("object")?;
    println!("{:?}", &value.borrow::<MyData>()? as *const _);
    println!("{:?}", &value.borrow::<MyData>()? as *const _);
    println!("{:?}", &value.borrow::<MyData>()? as *const _);

    Ok(())
}

fn main() {
    run().unwrap()
}

Output (example):

0x7ffe4c9944d0
0x7ffe4c9946a0
0x7ffe4c994870

So apparently I already tried this, but forgot about the details when I closed this issue five days ago.

The return type of borrow() is std::cell::Ref, so what the code above actually prints is the address of this instance of Ref.
Instead, I need to do the following (note the extra *) so that Ref is dereferenced and I actually take the address of the contained object:

    println!("{:?}", &value.borrow::<MyData>()? as *const _);

...and with this modification, things actually start working.

from rlua.