Enumerations

Enums must be exposed via UDL or proc-macros

Simple enums just work:

enum Animal {
    Dog,
    Cat,
}

and naturally used in the bindings:

Animal.Dog // kotlin

.dog // swift

Animal.DOG() # python
a.is_DOG()

Enums with fields

Enumerations with associated data are supported.

enum IpAddr {
  V4 {q1: u8, q2: u8, q3: u8, q4: u8},
  V6 {addr: string},
}

Enums can be very flexible (although UDL doesn't support all of this)

#[derive(uniffi::Enum)]
pub enum MyEnum {
    None,
    Str(String),
    All { s: String, i: i64 }
}

Remote, non-exhaustive enums

There are some special considerations here when using UDL

Methods on Enums.

proc-macros allow you to use #[uniffi::export] on an impl block for an enum. and the bindings will generate a method which calls into the Rust method. But take care - every time one of the methods is called, the entire enum will be copied by-value across the FFI.

Exposing methods from standard Rust traits

While less useful for Enums, there are a number of standard Rust traits (Debug, Eq etc) you can expose, so, eg, Python might generate __repr__() or __eq__() methods - see the docs for this feature.