3 unstable releases

Uses new Rust 2021

0.4.0 Aug 20, 2022
0.3.2 Aug 14, 2022
0.2.1 Aug 10, 2022
0.1.4-alpha.0 Aug 10, 2022

#733 in Procedural macros

45 downloads per month
Used in 2 crates (via minutus)

MIT license

711 lines


minutus docs.rs ci status license

Minutus is mruby binding for Rust, which enables you to treat mruby without writing painful boilerplates. Heavily inspired by Magnus.

By minutus, you can easily embed mruby in Rust, and create mrbgem by Rust.

Minutus also provides sensible type casting, and you can define typed functions on mruby values and wrap rust structs in mruby objects.

Embed mruby in Rust

Add minutus to your crate's dependencies.

cargo add minutus --features mruby_3_1_0,link_mruby

Write code like:

// src/main.rs

// This enables you to call `some_method` from Rust world.
  fn some_method(self, arr: Vec<i64>) -> i64;

fn main() {
    let runtime = minutus::Evaluator::build();

    // define `some_method` in mruby world
      def some_method(arr)
        p arr

    // capture mruby's main object
    let main = runtime.evaluate("self").unwrap();

    // call `some_method` on main object from Rust world.
    // in / out values are type-casted, according to `define_funcall!` definition
    let retval: i64 = main.some_method(vec![1,2,3,4]).unwrap();
    println!("retval is {}", retval);

Then, you can run your code:

$ cargo run
[1, 2, 3, 4]
retval is 10

If you want to use custom build_config.rb (e.g. for using mrbgems), you have to write custom build.rs

Minutus provides a helper for this purpose. See examples/custom-mruby.

Create mrbgem by Rust

Install minutus-mrbgem-template and initialize mrbgem.

$ cargo install minutus-mrbgem-template
$ minutus-mrbgem-template mruby-example
$ tree mruby-example
├── Cargo.lock
├── Cargo.toml
├── README.md
├── Rakefile
├── mrbgem.rake
├── mrblib
│   └── mrb_example.rb
├── mruby-example.gem
├── src
│   ├── dummy.c
│   └── lib.rs
└── test
    └── mrb_example.rb

Now, you can build and test mrbgem.

$ cd mruby-example && rake test
  Total: 1456
     OK: 1449
     KO: 0
  Crash: 0
Warning: 0
   Skip: 7
   Time: 0.06 seconds

Wrap Rust Structs in mruby Objects

You can wrap Rust's struct in mruby objects.

The following example defines TestMrbgem class in mruby, which has class method new, and instance methods distance and name_with_prefix.

#[minutus::wrap(class_method = "new", method = "distance", method = "name_with_prefix")]
struct TestMrbgem {
    x: i64,
    y: i64,
    name: String,

impl TestMrbgem {
    pub fn new(x: i64, y: i64, name: String) -> Self {
        Self { x, y, name }

    pub fn distance(&self, other: &TestMrbgem) -> f64 {
        (((self.x - other.x).pow(2) + (self.y - other.y).pow(2)) as f64).sqrt()

    pub fn name_with_prefix(&self, prefix: String) -> String {
        [prefix, self.name.clone()].join("_")

Define typed functions on mruby values

Use define_funcall! macro.

minutus::define_funcall! {
    fn inspect(self) -> String;
    fn concat(self, other: Vec<&str>) -> Vec<String> => "+";

fn main() {
    let runtime = minutus::Evaluator::build();

    let mruby_array = runtime.evaluate("['aaa', 'bbb']").unwrap();
    assert_eq!("[\"aaa\", \"bbb\"]", mruby_array.inspect().unwrap());
    assert_eq!(vec![String::from("aaa"), String::from("bbb"), String::from("ccc")], mruby_array.concat(vec!["ccc"]).unwrap());

Type casting

See minutus/src/types for details.

Rust type mruby type
i8, i16, i32, i64, isize Integer
u8, u16, u32, u64, usize Integer
f32, f64 Float
String String
Option<T> T or nil
(T, U), (T, U, V), etc [T, U], [T, U, V], etc
Vec<T> Array
std::collections::HashMap<T, U> Hash
minutus::types::RSymbol Symbol
bool any object
MrbData (structs marked by minutus::wrap) corresponding class

Any value in mruby can be cast to Rust's bool. Rust's bool cast to mruby's true or false.

Supported mruby versions

Currently, only 3.1.0 is supported. You can use mruby_master feature, but it is not guaranteed to work.


Minutus is an antonym of Magnus, which means small.


~21K SLoC