return inner struct

[brentp]

Hi, a full main.rs is below, but in brief, how can I get outer.inner where inner itself is a struct. I tried it as a Arc<Mutex> but still get the error:

   Compiling example v0.1.0 (/home/brentp/src/pyo3_ref)
error[E0277]: the trait bound `Arc<Mutex<Inner>>: LuaUserData` is not satisfied
   --> src/lib.rs:28:12
    |
28  |         lp.add_field_method_get("inner", |_, this| Ok(this.inner));
    |            ^^^^^^^^^^^^^^^^^^^^ the trait `LuaUserData` is not implemented for `Arc<Mutex<Inner>>`
    |
    = help: the following other types implement trait `LuaUserData`:
              Arc<lock_api::mutex::Mutex<parking_lot::raw_mutex::RawMutex, T>>
              Arc<lock_api::rwlock::RwLock<parking_lot::raw_rwlock::RawRwLock, T>>
              Arc<Mutex<T>>
              Arc<RwLock<T>>
              Arc<T>
    = note: required for `Arc<Mutex<Inner>>` to implement `IntoLua<'_>`
note: required by a bound in `add_field_method_get`
   --> /home/brentp/.cargo/registry/src/index.crates.io-6f17d22bba15001f/mlua-0.9.1/src/userdata.rs:499:12
    |
496 |     fn add_field_method_get<M, R>(&mut self, name: impl AsRef<str>, method: M)
    |        -------------------- required by a bound in this associated function
...
499 |         R: IntoLua<'lua>;
    |            ^^^^^^^^^^^^^ required by this bound in `UserDataFields::add_field_method_get`

For more information about this error, try `rustc --explain E0277`.

use mlua::*;
use std::io;
use std::sync::{Arc, Mutex};

pub struct Inner {
    i: i32,
    j: i32,
}

pub struct Outer {
    inner: Arc<Mutex<Inner>>,
    a: i32,
    b: i32,
}

fn main() -> io::Result<()> {
    let lua = Lua::new();

    lua.register_userdata_type::<Inner>(|lp| {
        lp.add_field_method_get("i", |_, this| Ok(this.i));
        lp.add_field_method_get("j", |_, this| Ok(this.j));
    })
    .unwrap();

    lua.register_userdata_type::<Outer>(|lp| {
        lp.add_field_method_get("a", |_, this| Ok(this.a));
        lp.add_field_method_get("b", |_, this| Ok(this.b));
        lp.add_field_method_get("inner", |_, this| Ok(this.inner));
    })
    .unwrap();

    Ok(())
}

thanks in advance. A repo with this example is here

[khvzak]

You need to change

lp.add_field_method_get("inner", |_, this| Ok(this.inner));

to

lp.add_field_method_get("inner", |lua, this| lua.create_any_userdata(this.inner.clone()));

This is needed because IntoLua is defined for T: UserData (but T=Inner itself does not implement this trait).
Alternative - impl UserData for Inner {}

Also in the case of manually registred type you need to register real inner type (not needed when impl UserData is used):

lua.register_userdata_type::<Arc<Mutex<Inner>>(...);

[brentp]

Thanks very much, indeed that makes sense for the lua.create_any_userdata and for registering Arc<Mutex<T>> instead of simply <T>.

I have it working as you suggest in the same repo/branch.