Synapse

Rust-to-SwiftUI Meta-Compiler

A Zig-based code generator that bridges the Rust↔Swift divide. Write your domain models once in Rust, get type-safe SwiftUI ViewModels automatically.

The Problem

Most developers: 1. Write Rust logic 2. Manually write Swift wrappers 3. Apple releases iOS 18, deprecates @StateObject for @Observable 4. Spend 3 weeks rewriting 50 files manually

This is Slop.

The Solution

With Synapse: 1. Update swift_templates.zig line 12 2. Run just gen-ui 3. Entire app upgraded to latest iOS standards instantly

You’ve effectively decoupled your IP (Rust) from the whims of the platform (Apple).

Quick Start

= Build Synapse

just build

= Generate Swift from Rust

just gen-ui

= Check the output

cat examples/swift/Generated.swift

Usage

1. Mark your Rust structs

#[derive(Synapse)]
pub struct PlayerState {
    pub coffee_count: i32,
    pub is_drifting: bool,
}

2. Run the generator

just gen-ui input=src/models.rs output=ios/Generated.swift

3. Use in SwiftUI

import SwiftUI

struct PlayerView: View {
    @State var model = PlayerStateViewModel()

    var body: some View {
        Text("Coffee: \(model.coffeeCount)")
    }
}

Commands

| Command | Description | |---------|-------------| | just build | Build the Synapse binary | | just gen-ui | Generate Swift ViewModels | | just gen-ui-legacy | Generate for iOS 14-16 | | just test | Run all tests | | just deploy-ios ~/MyApp | Generate and copy to Xcode project | | just help | Show CLI help |

Architecture

src/
├── generators/
│   └── synapse.zig      # Main entry point
├── parser/
│   └── rust_parser.zig  # Parses Rust struct definitions
└── templates/
    └── swift_templates.zig  # Apple Store compliance layer

Why Zig?

1. Text Processing: Handles string manipulation transparently (no lifetime gymnastics)

2. Compile Speed: Compiles instantly - code-gen runs in milliseconds

3. Bootstrap Separation: Outside the Rust dependency tree, no circular builds

Apple Store Compliance

The templates in swift_templates.zig define "Current Best Practice SwiftUI".

When Apple announces iOS 19 with new concurrency: 1. Update the template once 2. Run just gen-ui 3. Commit, upload to App Store

Your "Eternal Maintenance" problem is solved.

Supported Types

| Rust | Swift | |------|-------| | i32, i64 | Int, Int64 | | u32, u64 | UInt, UInt64 | | f32, f64 | Float, Double | | bool | Bool | | String | String | | Vec<T> | [T] | | Option<T> | T? | | Custom structs | Passed through |

Integration with UniFFI

Synapse complements UniFFI:

• UniFFI gives you data structures (struct Reef)

• Synapse gives you UI bindings (class ReefViewModel)

Use both together:

#[derive(uniffi::Object, Synapse)]  // Both!
pub struct Reef {
    pub lat: f64,
    pub lon: f64,
}

License

MIT

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"You describe the World in Rust, the Interface appears on iPhone."