luars

luars is an embeddable pure Rust Lua 5.5 runtime crate. It includes the compiler, VM, GC, standard library, and a high-level host API built around Lua.

If you want the repository-level overview, including examples and companion crates, start with ../../README.md. This README focuses on the crate surface that application code should use directly.

Installation

[dependencies]
luars = "0.18"

Optional features:

[dependencies]
luars = { version = "0.18", features = ["serde", "sandbox"] }

Quick Start

use luars::{Lua, SafeOption, Stdlib};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut lua = Lua::new(SafeOption::default());
    lua.load_stdlibs(Stdlib::All)?;

    lua.register_function("add", |a: i64, b: i64| a + b)?;
    let sum: i64 = lua.load("return add(1, 2)").eval()?;

    assert_eq!(sum, 3);
    Ok(())
}

High-Level Workflow

Execute code

lua.load("x = 40 + 2").exec()?;
let answer: i64 = lua.load("return x").eval()?;
let pair: (i64, i64) = lua.load("return 20, 22").eval_multi()?;

Call Lua globals

lua.load(
    r#"
    function greet(name)
        return "hello, " .. name
    end
    "#,
)
.exec()?;

let text: String = lua.call_global1("greet", "luars")?;

Register Rust functions

lua.register_function("slugify", |value: String| {
    value.trim().to_lowercase().replace(' ', "-")
})?;

Exchange tables and globals

let config = lua.create_table_from([("host", "127.0.0.1"), ("mode", "dev")])?;
lua.globals().set("config", config)?;

let globals = lua.globals();
let host: String = globals.get("config")?.get("host")?;
assert_eq!(host, "127.0.0.1");

Expose Rust types as userdata

use luars::{LuaUserData, lua_methods};

#[derive(LuaUserData)]
struct Counter {
    pub value: i64,
}

#[lua_methods]
impl Counter {
    pub fn new(value: i64) -> Self {
        Self { value }
    }

    pub fn inc(&mut self, delta: i64) {
        self.value += delta;
    }

    pub fn get(&self) -> i64 {
        self.value
    }
}

lua.register_type::<Counter>("Counter")?;
let count: i64 = lua
    .load(
        r#"
        local counter = Counter.new(1)
        counter:inc(41)
        return counter:get()
        "#,
    )
    .eval()?;

assert_eq!(count, 42);

Use scoped borrowed values

let result: String = lua.scope(|scope| {
    let prefix = String::from("user:");
    let format_name = scope.create_function_with(&prefix, |prefix: &String, value: String| {
        format!("{prefix}{value}")
    })?;

    scope.globals().set("format_name", &format_name)?;
    scope.load("return format_name('alice')").eval()
})?;

assert_eq!(result, "user:alice");

Async And Sandbox

The high-level API supports both typed async callbacks and async execution entry points:

lua.register_async_function("double_async", |value: i64| async move {
    Ok(value * 2)
})?;

let result: i64 = lua.load("return double_async(21)").eval_async().await?;
assert_eq!(result, 42);

You can also drive existing Lua functions asynchronously with call_async(), call_async1(), call_async_global(), and call_async_global1().

When the sandbox feature is enabled, the same high-level surface exposes isolated execution helpers:

use luars::SandboxConfig;

let mut sandbox = SandboxConfig::default();
lua.sandbox_insert_global(&mut sandbox, "answer", 42_i64)?;

let answer: i64 = lua.eval_sandboxed("return answer", &sandbox)?;
assert_eq!(answer, 42);

For more detail, see ../../docs/Async.md.

Feature Flags

Feature	Description
serde	Enable serde-based conversions
sandbox	Enable sandbox execution helpers
shared-proto	Enable shared prototypes for multi-VM scenarios

Known Boundaries

• No C API and no direct loading of native C Lua modules
• string.dump produces luars-specific bytecode
• Some corners of debug, io, and package still differ from the official C Lua implementation

See ../../docs/Different.md for the detailed compatibility notes.

Documentation

Document	Description
../../docs/Guide.md	High-level embedding guide
../../docs/UserGuide.md	High-level userdata guide
../../docs/Async.md	High-level async and sandbox guide
../../docs/Different.md	Known differences from C Lua

License

MIT. See ../../LICENSE.