How to handle Rust state?

[noib3]

Hi, this might be a noobish question. I'm writing a Rust plugin for Lua and I was wondering what's the best approach to handle state on the Rust side.

For a basic example, I'm trying to write a require('mymodule').plus_one() function that increments the field of a Rust struct every time it's called. This is what I have rn, which doesn't compile.

use mlua::{Lua, Result, Table};
use std::sync::{Arc, Mutex};

struct State {
    foo: usize,
}

fn plus_one(state: &mut State) {
    state.foo += 1;
}

#[mlua::lua_module]
fn mymodule(lua: &Lua) -> Result<Table> {
    let state = Arc::new(Mutex::new(State { foo: 0 }));
    let state = &mut state.lock().unwrap();

    let plus_one = lua.create_function(|_, ()| Ok(plus_one(state)))?;

    let exports = lua.create_table()?;

    // Should increment `state.foo` by 1 on every `require('mymodule').plus_one()` call
    exports.set("plus_one", plus_one)?;
    Ok(exports)
}

[khvzak]

You could rewrite your code as:

use mlua::{Lua, Result, Table};
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::Arc;

struct State {
    foo: AtomicUsize,
}

fn plus_one(state: &State) {
    state.foo.fetch_add(1, Ordering::Relaxed);
}

#[mlua::lua_module]
fn mymodule(lua: &Lua) -> Result<Table> {
    let state = Arc::new(State {
        foo: AtomicUsize::new(0),
    });

    let state2 = Arc::clone(&state);
    let plus_one = lua.create_function(move |_, ()| Ok(plus_one(&*state2)))?;

    let exports = lua.create_table()?;

    // Should increment `state.foo` by 1 on every `require('mymodule').plus_one()` call
    exports.set("plus_one", plus_one)?;
    Ok(exports)
}

or simply create a static global state available from any Rust function.