copyWith with nullable and optional

copywith_nullable.dart

 
/// General demonstration about the annoying way to set to null a copy of another object
///
/// @see https://github.com/dart-lang/language/issues/877
/// @see https://stackoverflow.com/questions/68009392/dart-custom-copywith-method-with-nullable-properties
class Person {
  final String name;
  final String? nickName;

  Person({required this.name, this.nickName});

  /// https://dart.dev/language/records#record-types
  Person copyWith({String? name, (String?,)? nickName}) {
    return Person(
      name: name ?? this.name,
      nickName: nickName != null ? (nickName.$1 ?? this.nickName) : null,
    );
  }
}

void main() {
  final a = Person(name: 'Amadeus', nickName: 'Momo');
  assert(a.nickName == 'Momo');

  final b = a.copyWith(nickName: (null));
  assert(b.nickName == null);
}