Awesome
Magnus
High level Ruby bindings for Rust. Write Ruby extension gems in Rust, or call Ruby code from a Rust binary.
Getting Started | Type Conversions | Safety | Compatibility
Examples
Defining Methods
Using Magnus, regular Rust functions can be bound to Ruby as methods with
automatic type conversion. Callers passing the wrong arguments or incompatible
types will get the same kind of ArgumentError
or TypeError
they are used to
seeing from Ruby's built in methods.
Defining a function (with no Ruby self
argument):
fn fib(n: usize) -> usize {
match n {
0 => 0,
1 | 2 => 1,
_ => fib(n - 1) + fib(n - 2),
}
}
#[magnus::init]
fn init(ruby: &magnus::Ruby) -> Result<(), Error> {
ruby.define_global_function("fib", magnus::function!(fib, 1));
Ok(())
}
Defining a method (with a Ruby self
argument):
fn is_blank(rb_self: String) -> bool {
!rb_self.contains(|c: char| !c.is_whitespace())
}
#[magnus::init]
fn init(ruby: &magnus::Ruby) -> Result<(), Error> {
// returns the existing class if already defined
let class = ruby.define_class("String", ruby.class_object())?;
// 0 as self doesn't count against the number of arguments
class.define_method("blank?", magnus::method!(is_blank, 0))?;
Ok(())
}
Calling Ruby Methods
Some Ruby methods have direct counterparts in Ruby's C API and therefore in
Magnus. Ruby's Object#frozen?
method is available as
magnus::ReprValue::check_frozen
, or Array#[]
becomes magnus::RArray::aref
.
Other Ruby methods that are defined only in Ruby must be called with
magnus::ReprValue::funcall
. All of Magnus' Ruby wrapper types implement the
ReprValue
trait, so funcall
can be used on all of them.
let s: String = value.funcall("test", ())?; // 0 arguments
let x: bool = value.funcall("example", ("foo",))?; // 1 argument
let i: i64 = value.funcall("other", (42, false))?; // 2 arguments, etc
funcall
will convert return types, returning Err(magnus::Error)
if the type
conversion fails or the method call raised an error. To skip type conversion
make sure the return type is magnus::Value
.
Wrapping Rust Types in Ruby Objects
Rust structs and enums can be wrapped in Ruby objects so they can be returned to Ruby.
Types can opt-in to this with the magnus::wrap
macro (or by implementing
magnus::TypedData
). Whenever a compatible type is returned to Ruby it will be
wrapped in the specified class, and whenever it is passed back to Rust it will
be unwrapped to a reference.
use magnus::{function, method, prelude::*, Error, Ruby};
#[magnus::wrap(class = "Point")]
struct Point {
x: isize,
y: isize,
}
impl Point {
fn new(x: isize, y: isize) -> Self {
Self { x, y }
}
fn x(&self) -> isize {
self.x
}
fn y(&self) -> isize {
self.y
}
fn distance(&self, other: &Point) -> f64 {
(((other.x - self.x).pow(2) + (other.y - self.y).pow(2)) as f64).sqrt()
}
}
#[magnus::init]
fn init(ruby: &Ruby) -> Result<(), Error> {
let class = ruby.define_class("Point", ruby.class_object())?;
class.define_singleton_method("new", function!(Point::new, 2))?;
class.define_method("x", method!(Point::x, 0))?;
class.define_method("y", method!(Point::y, 0))?;
class.define_method("distance", method!(Point::distance, 1))?;
Ok(())
}
The newtype pattern and RefCell
can be used if mutability is required:
struct Point {
x: isize,
y: isize,
}
#[magnus::wrap(class = "Point")]
struct MutPoint(std::cell::RefCell<Point>);
impl MutPoint {
fn set_x(&self, i: isize) {
self.0.borrow_mut().x = i;
}
}
To allow wrapped types to be subclassed they must implement Default
, and
define and alloc func and an initialize method:
#[derive(Default)]
struct Point {
x: isize,
y: isize,
}
#[derive(Default)]
#[wrap(class = "Point")]
struct MutPoint(RefCell<Point>);
impl MutPoint {
fn initialize(&self, x: isize, y: isize) {
let mut this = self.0.borrow_mut();
this.x = x;
this.y = y;
}
}
#[magnus::init]
fn init(ruby: &Ruby) -> Result<(), Error> {
let class = ruby.define_class("Point", ruby.class_object()).unwrap();
class.define_alloc_func::<MutPoint>();
class.define_method("initialize", method!(MutPoint::initialize, 2))?;
Ok(())
}
Getting Started
Writing an extension gem (calling Rust from Ruby)
Ruby extensions must be built as dynamic system libraries, this can be done by
setting the crate-type
attribute in your Cargo.toml
.
Cargo.toml
[lib]
crate-type = ["cdylib"]
[dependencies]
magnus = "0.7"
When Ruby loads your extension it calls an 'init' function defined in your
extension. In this function you will need to define your Ruby classes and bind
Rust functions to Ruby methods. Use the #[magnus::init]
attribute to mark
your init function so it can be correctly exposed to Ruby.
src/lib.rs
use magnus::{function, Error, Ruby};
fn distance(a: (f64, f64), b: (f64, f64)) -> f64 {
((b.0 - a.0).powi(2) + (b.1 - a.1).powi(2)).sqrt()
}
#[magnus::init]
fn init(ruby: &Ruby) -> Result<(), Error> {
ruby.define_global_function("distance", function!(distance, 2));
}
If you wish to package your extension as a Gem, we recommend using the
rb_sys
gem to build along with rake-compiler
. These tools will
automatically build your Rust extension as a dynamic library, and then package
it as a gem.
Note: The newest version of rubygems does have beta support for compiling
Rust, so in the future the rb_sys
gem won't be necessary.
my_example_gem.gemspec
spec.extensions = ["ext/my_example_gem/extconf.rb"]
# needed until rubygems supports Rust support is out of beta
spec.add_dependency "rb_sys", "~> 0.9.39"
# only needed when developing or packaging your gem
spec.add_development_dependency "rake-compiler", "~> 1.2.0"
Then, we add an extconf.rb
file to the ext
directory. Ruby will execute
this file during the compilation process, and it will generate a Makefile
in
the ext
directory. See the rb_sys
gem for more information.
ext/my_example_gem/extconf.rb
require "mkmf"
require "rb_sys/mkmf"
create_rust_makefile("my_example_gem/my_example_gem")
See the rust_blank
example for examples if extconf.rb
and Rakefile
.
Running rake compile
will place the extension at
lib/my_example_gem/my_example_gem.so
(or .bundle
on macOS), which you'd
load from Ruby like so:
lib/my_example_gem.rb
require_relative "my_example_gem/my_example_gem"
For a more detailed example (including cross-compilation and more), see the
rb-sys
example project. Although the code in lib.rs
does not feature
magnus, but it will compile and run properly.
Embedding Ruby in Rust
To call Ruby from a Rust program, enable the embed
feature:
Cargo.toml
[dependencies]
magnus = { version = "0.7", features = ["embed"] }
This enables linking to Ruby and gives access to the embed
module.
magnus::embed::init
must be called before calling Ruby and the value it
returns must not be dropped until you are done with Ruby. init
can not be
called more than once.
src/main.rs
use magnus::eval;
fn main() {
magnus::Ruby::init(|ruby| {
let val: f64 = eval!(ruby, "a + rand", a = 1)?;
println!("{}", val);
Ok(())
}).unwrap();
}
Type Conversions
Magnus will automatically convert between Rust and Ruby types, including
converting Ruby exceptions to Rust Result
s and vice versa.
These conversions follow the pattern set by Ruby's core and standard libraries,
where many conversions will delegate to a #to_<type>
method if the object is
not of the requested type, but does implement the #to_<type>
method.
Below are tables outlining many common conversions. See the Magnus api documentation for the full list of types.
Rust functions accepting values from Ruby
See magnus::TryConvert
for more details.
Rust function argument | accepted from Ruby |
---|---|
i8 ,i16 ,i32 ,i64 ,isize , magnus::Integer | Integer , #to_int |
u8 ,u16 ,u32 ,u64 ,usize | Integer , #to_int |
f32 ,f64 , magnus::Float | Float , Numeric |
String , PathBuf , char , magnus::RString , bytes::Bytes ‡ | String , #to_str |
magnus::Symbol | Symbol , #to_sym |
bool | any object |
magnus::Range | Range |
magnus::Encoding , magnus::RbEncoding | Encoding , encoding name as a string |
Option<T> | T or nil |
(T, U) , (T, U, V) , etc | [T, U] , [T, U, V] , etc, #to_ary |
[T; N] | [T] , #to_ary |
magnus::RArray | Array , #to_ary |
magnus::RHash | Hash , #to_hash |
std::time::SystemTime , magnus::Time , chrono::DateTime<T> § | Time |
magnus::Value | any object |
Vec<T> * | [T] , #to_ary |
HashMap<K, V> * | {K => V} , #to_hash |
&T , typed_data::Obj<T> where T: TypedData † | instance of <T as TypedData>::class() |
* when converting to Vec
and HashMap
the types of T
/K
,V
must be native Rust types.
† see the wrap
macro.
‡ when the bytes
feature is enabled
§ when the chrono
feature is enabled; T
can be Utc
or FixedOffset
.
Rust returning / passing values to Ruby
See magnus::IntoValue
for more details, plus magnus::method::ReturnValue
and magnus::ArgList
for some additional details.
returned from Rust / calling Ruby from Rust | received in Ruby |
---|---|
i8 ,i16 ,i32 ,i64 ,isize | Integer |
u8 ,u16 ,u32 ,u64 ,usize | Integer |
f32 , f64 | Float |
String , &str , char , &Path , PathBuf | String |
bool | true /false |
() | nil |
Range , RangeFrom , RangeTo , RangeInclusive | Range |
Option<T> | T or nil |
Result<T, magnus::Error> (return only) | T or raises error |
(T, U) , (T, U, V) , etc, [T; N] , Vec<T> | Array |
HashMap<K, V> | Hash |
std::time::SystemTime | Time |
T , typed_data::Obj<T> where T: TypedData * | instance of <T as TypedData>::class() |
* see the wrap
macro.
Conversions via Serde
Rust types can also be converted to Ruby, and vice versa, using Serde with
the serde_magnus
crate.
Manual Conversions
There may be cases where you want to bypass the automatic type conversions, to
do this use the type magnus::Value
and then manually convert or type check
from there.
For example, if you wanted to ensure your function is always passed a UTF-8 encoded String so you can take a reference without allocating you could do the following:
fn example(ruby: &Ruby, val: magnus::Value) -> Result<(), magnus::Error> {
// checks value is a String, does not call #to_str
let r_string = RString::from_value(val)
.ok_or_else(|| magnus::Error::new(ruby.exception_type_error(), "expected string"))?;
// error on encodings that would otherwise need converting to utf-8
if !r_string.is_utf8_compatible_encoding() {
return Err(magnus::Error::new(
ruby.exception_encoding_error(),
"string must be utf-8",
));
}
// RString::as_str is unsafe as it's possible for Ruby to invalidate the
// str as we hold a reference to it. The easiest way to ensure the &str
// stays valid is to avoid any other calls to Ruby for the life of the
// reference (the rest of the unsafe block).
unsafe {
let s = r_string.as_str()?;
// ...
}
Ok(())
}
Safety
When using Magnus, in Rust code, Ruby objects must be kept on the stack. If objects are moved to the heap the Ruby GC can not reach them, and they may be garbage collected. This could lead to memory safety issues.
It is not possible to enforce this rule in Rust's type system or via the borrow checker, users of Magnus must maintain this rule manually.
An example of something that breaks this rule would be storing a Ruby object in
a Rust heap allocated data structure, such as Vec
, HashMap
, or Box
. This
must be avoided at all costs.
While it would be possible to mark any functions that could expose this unsafty
as unsafe
, that would mean that almost every interaction with Ruby would
be unsafe
. This would leave no way to differentiate the really unsafe
functions that need much more care to use.
Other than this, Magnus strives to match Rust's usual safety guaranties for
users of the library. Magnus itself contains a large amount of code marked with
the unsafe
keyword, it is impossible to interact with Ruby's C-api without
this, but users of Magnus should be able to do most things without needing to
use unsafe
.
Compatibility
Ruby versions 3.0, 3.1, 3.2, and 3.3 are fully supported.
Magnus currently works with, and is still tested against, Ruby 2.7, but as this version of the language is no longer supported by the Ruby developers it is not recommended and future support in Magnus is not guaranteed.
Ruby bindings will be generated at compile time, this may require libclang to be installed.
The Minimum supported Rust version is currently Rust 1.61.
Support for statically linking Ruby is provided via the lower-level rb-sys
crate, and can be enabled by adding the following to your Cargo.toml
:
# * should select the same version used by Magnus
rb-sys = { version = "*", default-features = false, features = ["ruby-static"] }
Cross-compilation is supported by rb-sys for the platforms listed here.
Magnus is not tested on 32 bit systems. Efforts are made to ensure it compiles. Patches are welcome.
Crates that work with Magnus
rb-sys
Magnus uses rb-sys to provide the low-level bindings to Ruby. The
rb-sys
feature enables the rb_sys
module for
advanced interoperability with rb-sys, allows you to access low-level Ruby APIs
which Magnus does not expose.
serde_magnus
serde_magnus
integrates Serde and Magnus for seamless serialisation and
deserialisation of Rust to Ruby data structures and vice versa.
Users
halton
a Ruby gem providing a highly optimised method for generating Halton sequences.
Please open a pull request if you'd like your project listed here.
Troubleshooting
Issues with static linking
If you encounter an error such as symbol not found in flat namespace '_rb_ext_ractor_safe'
when embedding static Ruby, you will need to instruct
Cargo not to strip code that it thinks is dead.
In you the same directory as your Cargo.toml
file, create a
.cargo/config.toml
file with the following contents:
[build]
# Without this flag, when linking static libruby, the linker removes symbols
# (such as `_rb_ext_ractor_safe`) which it thinks are dead code... but they are
# not, and they need to be included for the `embed` feature to work with static
# Ruby.
rustflags = ["-C", "link-dead-code=on"]
Naming
Magnus is named after Magnus the Red a character from the Warhammer 40,000 universe. A sorcerer who believed he could tame the psychic energy of the Warp. Ultimately, his hubris lead to his fall to Chaos, but let's hope using this library turns out better for you.
License
This project is licensed under the MIT license, see LICENSE.