Attribute Macro ffi 

#[ffi]

Available on crate feature prelude only.

Generate FFI bindings between Rust and native platforms (Swift/Kotlin)

This attribute macro parses an extern "Swift" or extern "Kotlin" block and generates:

1. Opaque type wrappers for foreign types
2. Function implementations with direct JNI/ObjC bindings
3. Linker metadata for the CLI to compile the native source

Syntax

#[manganis::ffi("/src/ios")]
extern "Swift" {
    pub type GeolocationPlugin;
    pub fn get_position(this: &GeolocationPlugin, high_accuracy: bool) -> Option<String>;
}

#[manganis::ffi("/src/android")]
extern "Kotlin" {
    pub type GeolocationPlugin;
    pub fn get_position(this: &GeolocationPlugin, high_accuracy: bool) -> Option<String>;
}

Path Parameter

The path in the attribute specifies the native source folder relative to CARGO_MANIFEST_DIR:

• For Swift: A SwiftPM package folder containing Package.swift
• For Kotlin: A Gradle project folder containing build.gradle.kts

Type Declarations

Use type Name; to declare opaque foreign types. These become Rust structs wrapping the native object handle (GlobalRef for JNI, raw pointer for ObjC).

Function Declarations

Functions can be:

• Instance methods: First argument is this: &TypeName
• Static methods: No this argument

Supported Types

• Primitives: bool, i8-i64, u8-u64, f32, f64
• Strings: String, &str
• Options: Option<T> where T is supported
• Opaque refs: &TypeName for foreign type references