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Manual arbitrary Rust type

info

Usually the automatic arbitrary Rust type is sufficient. However, if you somehow want lower-level control, here is the type for you.

Example​

Rust:

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);
opaque.dispose();

Trait objects​

Trait objects can be put behind opaque pointers. For example, this declaration can be used across the FFI border:

pub struct DebugWrapper(pub RustOpaque<Box<dyn Debug>>);

// creating a DebugWrapper using the opaque_dyn macro
let wrap = DebugWrapper(opaque_dyn!("foobar"));
// it's possible to name it directly
pub struct DebugWrapper2(pub RustOpaque<Box<dyn Debug + Send + Sync + UnwindSafe + RefUnwindSafe>>);

Naming the inner type​

When an RustOpaque<T> is transformed into a Dart type, T's string representation undergoes some transformations to become a valid Dart type:

  • Rust keywords (dyn, 'static, etc.) are automatically removed.
  • ASCII alphanumerics are kept, all other characters are ignored.

Implementation details​

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