cloning-objects-in-dart.dart

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class Person {
  final Map<String, Object> _values;
  static const FIRST_NAME_KEY = 'FIRST_NAME';
  static const LAST_NAME_KEY = 'LAST_NAME';

  Person.from(Map<String, Object> props) : _values = props;

  Person({
    required String firstName,
    required String lastName,
    Map<String, Object>? props,
  }) : _values = {
          FIRST_NAME_KEY: firstName,
          LAST_NAME_KEY: lastName,
        };

  @override
  bool operator ==(covariant Person other) =>
      other.firstName == firstName && other.lastName == lastName;

  @override
  String toString() => _values.toString();
}

extension Properties on Person {
  String get firstName => _values[Person.FIRST_NAME_KEY].toString();
  set firstName(String newValue) => _values[Person.FIRST_NAME_KEY] = newValue;

  String get lastName => _values[Person.LAST_NAME_KEY].toString();
  set lastName(String newValue) => _values[Person.LAST_NAME_KEY] = newValue;
}

extension Clone on Person {
  Person clone([Map<String, Object>? additionalProps]) =>
      Person.from(Map.from(_values)..addAll(additionalProps ?? {}));
}

extension Subscripts on Person {
  Object? operator [](String key) => _values[key];
  operator []=(String key, Object value) => _values[key] = value;
}

void testIt() {
  final foo = Person(
    firstName: 'Foo Firstname',
    lastName: 'Foo Lastname',
  );
  print(foo); // {FIRST_NAME: Foo Firstname, LAST_NAME: Foo Lastname}
  final copyOfFoo = foo.clone();
  print(copyOfFoo); // {FIRST_NAME: Foo Firstname, LAST_NAME: Foo Lastname}
  final bar = foo.clone({'age': 30});
  print(bar); // {FIRST_NAME: Foo Firstname, LAST_NAME: Foo Lastname, age: 30}
  assert(foo == copyOfFoo);
  assert(foo == bar);
  assert(foo['age'] == null);
  assert(copyOfFoo['age'] == null);
  assert(bar['age'] == 30);
}