Functions

Functions are exposed in a namespace, either via UDL or proc-macros

#[uniffi::export] // if using proc-macros
fn hello_world() -> String {
    "Hello World!".to_owned()
}

Note that everything described here applies to all "callables" - eg, interface methods, constructors etc.

Optional arguments & default values

You can specify a default value for function arguments (in UDL and proc-macros)

The Rust code will still take a required argument:

fn hello_name(name: String) -> String {
    format!("Hello {}", name)
}

The generated foreign-language bindings will use function parameters with default values.

If the default argument value is "world", the generated Kotlin code will be equivalent to:

fun helloName(name: String = "world" ): String {
    // ...
}

Async functions "just work" with proc-macros, while UDL can use the [Async] attribute: