Minutus

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

You can embed mruby code in Rust code.

Add minutus to your crate's dependencies with link_mruby feature.

cargo add minutus --features link_mruby

Write code like:

// src/main.rs

// This enables you to call `some_method` in mruby world.
minutus::define_funcall!{
  fn some_method(self, arr: Vec<i64>) -> i64;
}

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

    // Define `some_method` in mruby world
    runtime.evaluate(
      "
      def some_method(arr)
        p arr
        arr.reduce(&:+)
      end
      "
    ).unwrap();

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

    // Call `some_method` on main object.
    // Arguments and return values are automatically 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] // in mruby workd
retval is 10 // in rust world

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
mruby-example
├── Cargo.lock
├── Cargo.toml
├── LICENSE
├── 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 {
    #[minutus::class_method]
    pub fn new(x: i64, y: i64, name: String) -> Self {
        Self { x, y, name }
    }

    #[minutus::method]
    pub fn distance(&self, other: &TestMrbgem) -> f64 {
        (((self.x - other.x).pow(2) + (self.y - other.y).pow(2)) as f64).sqrt()
    }

    #[minutus::method]
    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

3.1.0 and 3.2.0 are supported. You can also use mruby's master branch, but it is not tested.

If the version is not specified on Cargo.toml, the latest supported stable version is used.

[dependencies]
# Use 3.2.0
minutus = "*"

# Use 3.1.0
minutus = { version = "*", features = ["mruby_3_1_0"] }

# Use master branch
minutus = { version = "*", features = ["mruby_master"] }

Naming

Minutus is an antonym of Magnus, which means small.