swift-bridge

swift-bridge facilitates Rust and Swift interop.

swift-bridge makes it easy to pass and share high-level types between Rust and Swift, such as String, Option<T>, Result<T, E>, struct, class and more.

It also helps you bridge higher level language features, such as async functions and generics.

Using swift-bridge should be safer, more performant and more ergonomic than managing Rust and Swift FFI by hand.

Installation

# In your Cargo.toml

[build-dependencies]
swift-bridge-build = "0.1"

[dependencies]
swift-bridge = "0.1"

Book

You can find information about using Rust and Swift together in The swift-bridge Book.

Quick Peek

You use swift-bridge by declaring the types and functions that you want to import and export in a "bridge module", and then annotating that bridge module with the #[swift_bridge::bridge] macro.

Then, at build time, you use either the swift-bridge-build API or the swift-bridge-cli CLI to parse your annotated bridge modules and generate the Swift and C side of the FFI layer.

Here's a quick peek at how you might describe an FFI boundary between Swift and Rust using a bridge module.

// We use the `swift_bridge::bridge` macro to declare a bridge module.
// Then at build time the `swift-bridge-build` crate is used to generate
// the corresponding Swift and C FFI glue code.
#[swift_bridge::bridge]
mod ffi {
    // Create "transparent" structs where both Rust and Swift can directly access the fields.
    struct AppConfig {
        file_manager: CustomFileManager,
    }

    // Transparent enums are also supported.
    enum UserLookup {
        ById(UserId),
        ByName(String),
    }

    // Export opaque Rust types, functions and methods for Swift to use.
    extern "Rust" {
        type RustApp;

        #[swift_bridge(init)]
        fn new(config: AppConfig) -> RustApp;
        
        fn get_user(&self, lookup: UserLookup) -> Option<&User>;
    }

    extern "Rust" {
        type User;
        type MessageBoard;

        #[swift_bridge(get(&nickname))]
        fn informal_name(self: &User) -> &str;
    }

    // Import opaque Swift classes and functions for Rust to use.
    extern "Swift" {
        type CustomFileManager;
        fn save_file(&self, name: &str, contents: &[u8]);
    }
}

struct User {
    nickname: String
}

Quick Start

The swift-bridge repository contains example applications that you use to quickly try out the library, or as a starting point for your own Swift + Rust based application.

For example, here's how to run the codegen-visualizer example project locally.

git clone https://github.com/chinedufn/swift-bridge
cd swift-bridge/examples/codegen-visualizer

open CodegenVisualizer/CodegenVisualizer.xcodeproj
# *** Click the "Run" button at the top left of Xcode ***

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You can find information about using Rust and Swift together in The swift-bridge Book.

Built-In Types

In addition to allowing you to share your own custom structs, enums and classes between Rust and Swift, swift-bridge comes with support for a number of Rust and Swift standard library types.

name in Rust	name in Swift	notes
u8, i8, u16, i16... etc	UInt8, Int8, UInt16, Int16 ... etc
bool	Bool
String, &String, &mut String	RustString, RustStringRef, RustStringRefMut
&str	RustStr
Vec<T>	RustVec<T>
SwiftArray<T>	Array<T>	Not yet implemented
&[T]		Not yet implemented
&mut [T]		Not yet implemented
Box<T>		Not yet implemented
Box<dyn FnOnce(A,B,C) -> D>	(A, B, C) -> D	Passing from Rust to Swift is supported, but Swift to Rust is not yet implemented.
Box<dyn Fn(A,B,C) -> D>	(A, B, C) -> D	Not yet implemented
Arc<T>		Not yet implemented
[T; N]		Not yet implemented
*const T	UnsafePointer<T>
*mut T	UnsafeMutablePointer<T>
Option<T>	Optional<T>
fn x() -> Result<T, E>	func x() throws -> T
fn x(arg: Result<T, E>)	func x(arg: RustResult<T, E>)
(A, B, C, ...)	(A, B, C, ...)
Have a Rust standard library type in mind? Open an issue!
	Have a Swift standard library type in mind? Open an issue!

Performance

swift-bridge aims to be useful in performance critical environments.

None of its generated FFI code uses object serialization, cloning, synchronization or any other form of unnecessary overhead.

To Test

To run the test suite.

# Clone the repository
git clone git@github.com:chinedufn/swift-bridge.git
cd swift-bridge

# Run tests
cargo test --all && ./test-swift-rust-integration.sh && ./test-swift-packages.sh 

Contributing

If you're interesting in contributing to swift-bridge, check out the contributor's guide.

After getting familiar with the contribution process, try looking at some of the good first issues to see if any peak your interest.

These issues come with step-by-step instructions that should help guide you towards implementing your first patch.

Acknowledgements

• cxx inspired the idea of using a bridge module to describe the FFI boundary.

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License

Licensed under MIT or Apache-2.0.