# Magnus
Ruby bindings for Rust. Write Ruby extension gems in Rust, or call Ruby code
from a Rust binary.
[API Docs]: https://docs.rs/magnus/latest/magnus/
[GitHub]: https://github.com/matsadler/magnus
[crates.io]: https://crates.io/crates/magnus
[Getting Started]: #getting-started
[Type Conversions]: #type-conversions
[Safety]: #safety
[Compatibility]: #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):
```rust
fn fib(n: usize) -> usize {
match n {
0 => 0,
1 | 2 => 1,
_ => fib(n - 1) + fib(n - 2),
}
}
magnus::define_global_function("fib", magnus::function!(fib, 1));
```
Defining a method (with a Ruby `self` argument):
```rust
fn is_blank(rb_self: String) -> bool {
!rb_self.contains(|c: char| !c.is_whitespace())
}
let class = magnus::define_class("String", Default::default())?;
// 0 as self doesn't count against the number of arguments
class.define_method("blank?", magnus::method!(is_blank, 0))?;
```
### 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::Value::check_frozen`, or `Array#[]` becomes `magnus::RArray::aref`.
Other Ruby methods that are defined only in Ruby must be called with
`magnus::Value::funcall`. All of Magnus' Ruby wrapper types deref to `Value`,
so `funcall` can be used on all of them.
```rust
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.
```rust
use magnus::{define_class, function, method, prelude::*, Error};
#[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() -> Result<(), Error> {
let class = define_class("Point", Default::default())?;
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:
```rust
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;
}
}
```
## 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`**
```toml
[lib]
crate-type = ["cdylib"]
[dependencies]
magnus = "0.4"
```
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`**
```rust
use magnus::{define_global_function, function};
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() {
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`**
```ruby
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`**
```ruby
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`**
```ruby
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.
[`rb-sys` gem]: https://github.com/oxidize-rb/rb-sys/tree/main/gem
[`rake-compiler`]: https://github.com/rake-compiler/rake-compiler
[`rust_blank`]: https://github.com/matsadler/magnus/tree/main/examples/rust_blank/ext/rust_blank
[`rb-sys` example project]: https://github.com/oxidize-rb/rb-sys/tree/main/examples/rust_reverse
### Embedding Ruby in Rust
To call Ruby from a Rust program, enable the `embed` feature:
**`Cargo.toml`**
```toml
[dependencies]
magnus = { version = "0.4", 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`**
```rust
use magnus::{embed, eval};
fn main() {
let _cleanup = unsafe { embed::init() };
let val: f64 = eval!("a + rand", a = 1).unwrap();
println!("{}", val);
}
```
## Type Conversions
Magnus will automatically convert between Rust and Ruby types, including
converting Ruby exceptions to Rust `Result`s and visa 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.
| `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` | `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` |
| `magnus::Value` | any object |
| `Vec<T>`* | `[T]`, `#to_ary` |
| `HashMap<K, V>`* | `{K => V}`, `#to_hash` |
| `&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.
### Rust returning / passing values to Ruby
See the `magnus::Value` type, for all types implementing `Into<Value>`, plus
`magnus::method::ReturnValue` and `magnus::ArgList` for some additional details.
| `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` |
| `T where T: TypedData`** | instance of `<T as TypedData>::class()` |
\** see the `wrap` macro.
### 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:
```rust
fn example(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::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::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.
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 2.7, 3.0, and 3.1 are fully supported.
Ruby 3.2 is (as of writing) in preview and support is provided, but not
guaranteed.
Magnus currently works with Ruby 2.6, 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 1.51 (Rust 1.54 on macOS
with Xcode 14).
Support for statically linking Ruby is provided.
Cross-compilation is supported by rb-sys [for the platforms listed here][plat].
Support for 32 bit systems is almost certainly broken, patches are welcome.
[plat]: https://github.com/oxidize-rb/rb-sys#supported-platforms
### rb-sys
Magnus uses [rb-sys] to provide the low-level bindings to Ruby. The
`rb-sys-interop` feature enables the
[`rb_sys`](https://docs.rs/magnus/latest/magnus/rb_sys/index.html) module for
advanced interoperability with rb-sys, allows you to access low-level Ruby APIs
which Magnus does not expose.
[rb-sys]: https://github.com/oxidize-rb/rb-sys/tree/main/crates/rb-sys
### 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:
```toml
[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"]
```
## Alternatives
* [rutie](https://github.com/danielpclark/rutie)
* [rosy](https://github.com/nvzqz/rosy)
* [ruby-sys](https://github.com/steveklabnik/ruby-sys)
* [ruru](https://github.com/d-unseductable/ruru)
* [plugger](https://github.com/dylanmckay/plugger)
* [helix](https://github.com/tildeio/helix)
## 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 lets hope using this
library turns out better for you.
## License
This project is licensed under the MIT license, see LICENSE.