Ruru (Rust + Ruby = :heart:)

Native Ruby extensions in Rust

Have you ever considered rewriting some parts of your slow Ruby application?

Just rewrite your Ruby application with Rust method by method, class by class. It does not require to change interface of your classes or to change any other Ruby code.

As simple as Ruby, as efficient as Rust.

Examples

The famous String#blank? method

#[no_mangle]
pub extern fn is_blank(_: Argc, _: *const AnyObject, itself: RString) -> Boolean {
    Boolean::new(itself.to_string().chars().all(|c| c.is_whitespace()))
}

fn main() {
    Class::from_existing("String").define(|itself| {
        itself.def("blank?", is_blank);
    });
}

Defining a new class

Let's say you have a Calculator class.

class Calculator
  def pow_3(number)
    (1..number).each_with_object({}) do |index, hash|
      hash[index] = index ** 3
    end
  end
end
# ... somewhere in the application ...
Calculator.new.pow_3(5) #=> { 1 => 1, 2 => 8, 3 => 27, 4 => 64, 5 => 125 }

You found it's very slow to call pow_3 for big number and decided to replace the whole class with Rust.

#[no_mangle]
pub extern fn pow_3(argc: Argc, argv: *const AnyObject, itself: Fixnum) -> Hash {
    let argv = VM::parse_arguments(argc, argv);
    let num = argv[0].as_fixnum().to_i64();

    let mut hash = Hash::new();

    for i in (1..num + 1) {
        hash.store(Fixnum::new(i), Fixnum::new(i.pow(3)));
    }

    hash
}

Class::new("Calculator").define(|itself| {
    itself.def("pow_3", pow_3);
});

Ruby:

# No Calculator class in Ruby anymore

# ... somewhere in the application ...
Calculator.new.pow_3(5) #=> { 1 => 1, 2 => 8, 3 => 27, 4 => 64, 5 => 125 }

So nothing has changed in the API of class thus no need to change code elsewhere in the app.

Replacing only several methods instead of the whole class

If the Calculator class from the example above has more methods Ruby methods, but we want to replace only pow_3, use Class::from_existing()

Class::from_existing("Calculator").define(|itself| {
    itself.def("pow_3", pow_3);
});

Calling Ruby code from Rust

Getting an account balance of some User whose name is John and who is 18 or 19 years old.

User
  .find_by(age: [18, 19], name: 'John')
  .account_balance

let mut conditions = Hash::new();

conditions.store(
    Symbol::new("age"),
    Array::new().push(Fixnum::new(18)).push(Fixnum::new(19))
);

conditions.store(
    Symbol::new("name"),
    RString::new("John")
);

let account_balance =
  Class::from_existing("User")
        .send("find_by", vec![conditions.as_any_object()])
        .send("account_balance")
        .as_fixnum()
        .to_i64();

... and why FFI is not enough?

• No support of native Ruby types;

• No way to create a standalone application to run Ruby VM separately;

• No way to call your Ruby code from Rust;

How to use?

Ruru requires rbenv to be installed. Building and linking process is automatic.

There are two ways of using Ruru:

• Standalone application - Rust is run first as a compiled executable file and then it calls Ruby code (see docs for VM::init())

• Running Rust code from Ruby application

The second way requires additional steps (to be improved):

1. Add Ruru to Cargo.toml

[dependencies]
ruru = ">= 0.5.0"

2. Compile your library as dylib

[lib]
crate-type = ["dylib"]

3. Create a function which will initialize

#[no_mangle]
pub extern fn initialize_my_app() {
    Class::new("SomeClass");

    /// ... etc
}

4. Open the library and call function from Ruby

require 'fiddle'

library = Fiddle::dlopen('libmy_library.dylib')

Fiddle::Function.new(library['init_my_app'], [], Fiddle::TYPE_VOIDP).call

5. Ruru is ready :heart: