Arbitrary Rust types (opaque)

On one hand, any Rust type, even if it is not supported using features of this library, can be used in Dart. This is done by wrapping it with RustOpaque.

The Rust opaque objects in Dart should be disposed manually, though it will also be disposed when it is GCed, that is discouraged, due to suggestions by Dart team. Think of it just like a lot of Flutter objects that we are familiar with, such as ui.Image - we have to manually dispose them as well.

Different from non-opaque types, opaque types are not copied/moved/reconstructed at all. For example, if you pass around RwLock<Mutex<ArbitraryData> in arguments and return values, you will get the exact same RwLock<ArbitraryData> object.

Example RustOpaque


struct ArbitraryData { ... }
pub fn use_opaque(a: RustOpaque<ArbitraryData>) { ... }
pub fn even_use_locks(b: RustOpaque<Mutex<ArbitraryData>) -> RustOpaque<RwLock<ArbitraryData>> { ... }
enum AnEnumContainingOpaque { Hello(RustOpaque<ArbitraryData>), World(i32) }

And use it in Dart:

var opaque = await api.functionThatCreatesSomeOpaqueData();
await api.functionThatUsesSomeOpaqueData(opaque);

Implementation details

As for how it is implemented as well as the design towards safety, please refer to this doc