[Dart] 복제된 객체의 copyWith 기본

[Dart] 객체 복사

보통 B=A로 복사(실패예)

class User {
  final String username;

  const User({this.username});
}

void main() {
  const userA = User(username: 'UserA');

  const userB = userA;
  print(userA.username + ':' + userA.hashCode.toString());
  print(userB.username + ':' + userA.hashCode.toString());
}

UserA:419201198
UserA:419201198

class User {
  final String username;

  const User({this.username});

  @override
  String toString() => username + ':' + hashCode.toString();
}

void main() {
  const userA = User(username: 'UserA');

  const userB = userA;
  print(userA.toString());
  print(userB.username + ':' + userA.hashCode.toString());
}

UserA:288318752
UserA:288318752

class User {
  final String username;

  const User({this.username});

  User copyWith({
    String username,
  }) =>
      User(
        username: username ?? this.username,
      );

  @override
  String toString() => username + ':' + hashCode.toString();
}

void main() {
  const userA = User(username: 'UserA');
  final userB = userA;
  print(userA.toString());
  print(userB.toString());
}

UserA:463513894
UserA:463513894

copyWith 함수 사용(성공 예)

class User {
  final String username;

  const User({this.username});

  User copyWith({
    String username,
  }) =>
      User(
        username: username ?? this.username,
      );

  @override
  String toString() => username + ':' + hashCode.toString();
}

void main() {
  const userA = User(username: 'UserA');
  final userB = userA.copyWith();
  final userC = userA.copyWith(username: 'UserC');
  print(userA.toString());
  print(userB.toString());
  print(userC.toString());
}

UserA:610790447
UserA:455007180
UserC:1059822335