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Type alias

Type alias is also supported. For example:

enum MyEnum {...}
struct MyStruct {...}

// type aliases
pub type Id = u64;
pub type EnumAlias = MyEnum;
pub type StructAlias = MyStruct;

// can also use them in fields, etc
pub struct TestModel { pub id: Id, pub e: EnumAlias, pub s: StructAlias}

pub fn f(input: Id) -> TestModel {...}

Generic type aliases​

Generic type aliases are expanded at the use site, so you can use them in exported signatures exactly like the underlying type. A common case is a project-wide fallible Result shortcut:

pub enum AppError {...}

pub type AppResult<T> = Result<T, AppError>;

// Equivalent to `-> Result<MyData, AppError>`: on the Dart side this returns
// `MyData` on success and throws a Dart exception carrying `AppError` on failure.
pub fn load_data() -> AppResult<MyData> {...}

The substitution is applied recursively, so aliases built on top of other generic aliases (for example pub type Wrapper<T> = Option<T>) work as well.

Limitation​

  • The ItemType inside Generic is not supported yet, such as SyncReturn<Id>. The nested ItemType may also not be supported. This also applies to generic aliases nested inside such wrappers (e.g. SyncReturn<AppResult<T>>).
  • Generic type aliases with lifetime parameters, const parameters, or a where clause are not yet supported.