im_model 1.4.0

Annotation for immutable model to generate `copyWith` and == (equal) operator.

Annotations and immutable collections for im_model_gen — a code generator that adds == equality and copyWith to your Dart classes.

Features

• Standard Dart syntax — no custom factories or sealed classes required
• Errors at generation time, not runtime
• Small generated output — smaller binary, faster IDE
• Enforces immutable collections
• Supports inheritance

Setup

# pubspec.yaml
dependencies:
  im_model: ^1.4.0

dev_dependencies:
  im_model_gen: ^1.4.0
  build_runner: ^2.0.0

Usage

Annotate your class, add the generated mixin, and declare the part file:

import 'package:im_model/im_model.dart';

part 'example.g.dart';

@ImModel()
class Example with _$ExampleMixin {
  final String id;
  final String? name;
  final ImList<int> values;

  const Example(this.id, {this.name, required this.values});
}

Run the generator:

dart run build_runner build

Then use the generated extensions:

const example = Example('id', values: ImList.empty());

// Copy with new values
example.copyWith(name: 'Alice'); // Example(id: id, name: Alice, values: [])
example.copyWith(name: null);   // Example(id: id, name: null,  values: [])

// Equality
const other = Example('id', values: ImList.empty());
example == other;                       // true
example == other.copyWith(values: [1]); // false

// Immutability — compile error:
// example.values.add(1); // 'add' is undefined

Annotations

@ImModel

Applied to a class.

Parameter	Default	Description
ignoreCopy	false	Skip copyWith generation
ignoreEqual	false	Skip == / hashCode generation
copyConstructor	null	Named constructor to use for copies

@ImField

Applied to a field to override the class-level @ImModel settings.

Parameter	Default	Description
ignoreCopy	false	Exclude this field from copyWith
ignoreEqual	false	Exclude this field from equality

Collections

Replace mutable collections with their immutable counterparts:

Mutable	Immutable
List<T>	ImList<T>
Map<K, V>	ImMap<K, V>
Set<T>	ImSet<T>

The generator emits an error if it detects a mutable collection.

Use .mut / .immut to switch between views — .mut is copy-on-write, so there's no allocation cost unless you actually modify it:

obj = obj.copyWith(values: obj.values.mut..add(42));
// Generated code wraps the result back to ImList automatically.

Elements inside collections are not checked. ImList<MyMutableClass> is still mutable.

vs Freezed

• No special factory constructors or @freezed class shape
• Mutable collections are caught at generation time
• Lean generated output
• No lock-in syntax — easy to migrate away from
• Generated code is intentionally minimal. A production Flutter web app (8.2 MB) saw a 650 KB reduction (~8% of main.dart.js) after migrating from Freezed.