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;
        type CustomIoError;

        // Async functions are supported.
        async fn save_file(self: &CustomFileManager, name: &str, contents: &[u8]) -> Result<(), CustomIoError>;
    }
}

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 ***

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.

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.

Minimum Supported Swift Version (MSSV)

swift-bridge currently guarantees that the Swift code that it generates will work on Swift 6.0 and later. This is known the project's "Minimum Supported Swift Version" (MSSV).

swift-bridge's current policy is that the minimum required Swift version can be increased at any time to any Swift version that is at least one month old.

For instance, if Swift 9.10.11 is released on April 5, 2035, then on May 5, 2035 the swift-bridge project is allowed to begin emitting Swift code that relies on Swift 9.10.11.

We will increase our support windows when one or both of the following happen:

• We are no longer waiting for Swift features that increase the safety, performance and ergonomics of the Swift code that swift-bridge emits.

• For instance, Swift recently introduced the ~Copyable protocol, which we plan to use enforce ownership when Swift code uses opaque Rust types.

• The short support window is disrupting projects that use swift-bridge today.

• Please open an issue if our MSSV policy impacts your project

Acknowledgements

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

License

Licensed under MIT or Apache-2.0.