mlua-rs-mlua/examples/module/src/lib.rs

use mlua::prelude::*;

fn sum(_: &Lua, (a, b): (i64, i64)) -> LuaResult<i64> {
    Ok(a + b)
}

fn used_memory(lua: &Lua, _: ()) -> LuaResult<usize> {
    Ok(lua.used_memory())
}

fn check_userdata(_: &Lua, ud: MyUserData) -> LuaResult<i32> {
    Ok(ud.0)
}

#[mlua::lua_module]
fn rust_module(lua: &Lua) -> LuaResult<LuaTable> {
    let exports = lua.create_table()?;
    exports.set("sum", lua.create_function(sum)?)?;
    exports.set("used_memory", lua.create_function(used_memory)?)?;
    exports.set("check_userdata", lua.create_function(check_userdata)?)?;
    Ok(exports)
}

#[derive(Clone, Copy)]
struct MyUserData(i32);

impl LuaUserData for MyUserData {}

#[mlua::lua_module]
fn rust_module_second(lua: &Lua) -> LuaResult<LuaTable> {
    let exports = lua.create_table()?;
    exports.set("userdata", lua.create_userdata(MyUserData(123))?)?;
    Ok(exports)
}

#[mlua::lua_module]
fn rust_module_error(_: &Lua) -> LuaResult<LuaTable> {
    Err("custom module error".to_lua_err())
}