maybe_copy_with 1.0.0

maybe_copy_with: ^1.0.0 copied to clipboard

example/lib/example.dart

import 'package:maybe_copy_with/maybe_copy_with.dart';

void main() {
  // Original instance
  final john = User(name: 'John', age: 18, gender: 'Male');

  // 1️⃣ Change a non‑nullable field — `gender` stays untouched
  final bob = john.copyWith(name: 'Bob');
  // or
  // final bob = john.copyWith(name: 'Bob', gender: null);

  // 2️⃣ Change both a non‑nullable and a nullable field
  final alice = bob.copyWith(
    name: 'Alice',
    gender: 'Female'.maybe(), // wrap with .maybe() to *replace* nullable field
  );

  // 3️⃣ Explicitly reset the nullable field to null
  final android = alice.copyWith(
    gender: null.maybe(), // set to null via .maybe()
  );

  print(john); // User(name: John, age: 18, gender: Male)
  print(bob); // User(name: Bob, age: 18, gender: Male)
  print(alice); // User(name: Alice, age: 18, gender: Female)
  print(android); // User(name: Alice, age: 18, gender: null)
}

class User with MaybeCopyWith<User> {
  final String name;
  final int age;
  final String? gender;

  const User({required this.name, required this.age, this.gender});

  /// Returns a **new** [User] where only the fields you specify are changed.
  ///
  /// * `name`, `age` – plain nullable params. Pass a new value to replace the
  ///   current one, or omit (leave `null`) to keep the existing value.
  /// * `gender` – wrapped in [Maybe] so you have **three** options:
  ///   * `null` or omit → keep current `gender` value;
  ///   * `'Female'.maybe()` → set a new non‑null value;
  ///   * `null.maybe()` → explicitly reset to `null`.
  @override
  User copyWith({String? name, int? age, Maybe<String>? gender}) => User(
    name: name ?? this.name,
    age: age ?? this.age,
    gender: gender.or(this.gender),
  );

  @override
  String toString() => 'User(name: $name, age: $age, gender: $gender)';
}