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Structs

Normal Rust structs are supported. You can even use recursive fields, such as pub struct TreeNode { pub value: String, pub children: Vec<MyTreeNode>, pub parent: Box<MyTreeNode> }.

For versions older than v1.66.0 (no need for latest version), if a struct field has type being a struct or an enum, please add a Box on it, or it will lead to compile-time error. For example, struct A {b: B} should be struct A {b: Box<B>} instead.

Tuple structs​

Tuple structs struct Foo(A, B) are translated as class Foo { A field0; B field1; }, since Dart does not have anonymous fields.

Non-final fields​

By adding #[frb(non_final)] to a field of struct, the corresponding field in Dart will be non-final. By default, we make all generated fields final because of Rust's philosophy - immutable by default.

Unless a field has been annotated with #[frb(non_final)], generated classes will also be const-constructible.

Dart metadata annotations​

You can add dart metadata annotations using dart_metadata parameter in frb macro.

  • For annotations that are prelude by dart (e.g. @deprecated), just put annotation as a Rust literal.
  • If importing is needed, then add importing part behind the annotation string. Currently two forms of importing supported:
    • import 'somepackage'
    • import 'somepackage' as somename, where somename will be the prefix of the annotation
  • Multiple annotations are separated by comma ,.

See below for an example.

freezed Dart classes​

If you want the generated Dart class to be freezed (which is like data-classes in other languages like Kotlin), simply put #[frb(dart_metadata=("freezed"))] and it will generate everything needed for you.

Rename fields​

The #[frb(name = "...")] can be utilized to change the Dart name of a struct field. For example:

#[frb]
pub struct MyStruct {
  #[frb(name = "dartFieldName")]
  pub rust_field_name: Vec<u8>,
}

It will give a Dart class with field dartFieldName.

Example​

Example 1: Recursive fields​

pub struct MyTreeNode {
    pub value: Vec<u8>,
    pub children: Vec<MyTreeNode>,
}

Becomes:

class MyTreeNode {
  final Uint8List value;
  final List<MyTreeNode> children;
  MyTreeNode({required this.value, required this.children});
}

Remark: If you are curious about Future, have a look at this.

Example 2: Metadata​

#[frb(dart_metadata=("freezed", "immutable" import "package:meta/meta.dart" as meta))]
pub struct UserId {
    pub value: u32,
}

Becomes:

import 'package:meta/meta.dart' as meta;

@freezed
@meta.immutable
class UserId with _$UserId {
  const factory UserId({
    required int value,
  }) = _UserId;
}