How can I clone an Object (deep copy) in Dart?

Question

Is there a Language supported way make a full (deep) copy of an Object in Dart?

Secondary only; are there multiple ways of doing this, and what are the differences?<

Answer 1

It only works for object types that can be represented by JSON.

ClassName newObj = ClassName.fromMap(obj.toMap());

or

ClassName newObj = ClassName.fromJson(obj.toJson());

Answer 2

Darts built-in collections use a named constructor called "from" to accomplish this. See this post: Clone a List, Map or Set in Dart

Map mapA = {
    'foo': 'bar'
};
Map mapB = new Map.from(mapA);

Answer 3

To copy an object without reference, the solution I found was similar to the one posted here, however if the object contains MAP or LIST you have to do it this way:

class Item {
  int id;
  String nome;
  String email;
  bool logado;
  Map mapa;
  List lista;
  Item({this.id, this.nome, this.email, this.logado, this.mapa, this.lista});

  Item copyWith({ int id, String nome, String email, bool logado, Map mapa, List lista }) {
    return Item(
      id: id ?? this.id,
      nome: nome ?? this.nome,
      email: email ?? this.email,
      logado: logado ?? this.logado,
      mapa: mapa ?? Map.from(this.mapa ?? {}),
      lista: lista ?? List.from(this.lista ?? []),
    );
  }
}

Item item1 = Item(
    id: 1,
    nome: 'João Silva',
    email: 'joaosilva@gmail.com',
    logado: true,
    mapa: {
      'chave1': 'valor1',
      'chave2': 'valor2',
    },
    lista: ['1', '2'],
  );

// -----------------
// copy and change data
Item item2 = item1.copyWith(
    id: 2,
    nome: 'Pedro de Nobrega',
    lista: ['4', '5', '6', '7', '8']
  );

// -----------------
// copy and not change data
Item item3 = item1.copyWith();

// -----------------
// copy and change a specific key of Map or List
Item item4 = item1.copyWith();
item4.mapa['chave2'] = 'valor2New';

See an example on dartpad

https://dartpad.dev/f114ef18700a41a3aa04a4837c13c70e

Answer 4

Trying using a Copyable interface provided by Dart.

Answer 5

Unfortunately no language support. What I did is to create an abstract class called copyable which I can implement in the classes I want to be able to copy:

abstract class Copyable<T> {
  T copy();
  T copyWith();
}

I can then use this as follows, e.g. for a Location object:

@override
Location copy() {
  return Location(
      longitude: this.longitude,
      latitude: this.latitude,
      timestamp: this.timestamp,
      country: this.country,
      locality: this.locality,
      postalCode: this.postalCode,
      name: this.name,
      isoCountryCode: this.isoCountryCode,
      bearing: this.bearing);
}

@override
Location copyWith({
    String country,
    String locality,
    String name
  }) {
  return Location(
      country: country,
      locality: locality,
      name: name,
      longitude: this.longitude,
      latitude: this.latitude,
      timestamp: this.timestamp,
      postalCode: this.postalCode,
      isoCountryCode: this.isoCountryCode,
      bearing: this.bearing);
}

Answer 6

An example of Deep copy in dart.

void main() {
  Person person1 = Person(
      id: 1001,
      firstName: 'John',
      lastName: 'Doe',
      email: 'john.doe@email.com',
      alive: true);

  Person person2 = Person(
      id: person1.id,
      firstName: person1.firstName,
      lastName: person1.lastName,
      email: person1.email,
      alive: person1.alive);

  print('Object: person1');
  print('id     : ${person1.id}');
  print('fName  : ${person1.firstName}');
  print('lName  : ${person1.lastName}');
  print('email  : ${person1.email}');
  print('alive  : ${person1.alive}');
  print('=hashCode=: ${person1.hashCode}');

  print('Object: person2');
  print('id     : ${person2.id}');
  print('fName  : ${person2.firstName}');
  print('lName  : ${person2.lastName}');
  print('email  : ${person2.email}');
  print('alive  : ${person2.alive}');
  print('=hashCode=: ${person2.hashCode}');
}

class Person {
  int id;
  String firstName;
  String lastName;
  String email;
  bool alive;
  Person({this.id, this.firstName, this.lastName, this.email, this.alive});
}

And the output below.

id     : 1001
fName  : John
lName  : Doe
email  : john.doe@email.com
alive  : true
=hashCode=: 515186678

Object: person2
id     : 1001
fName  : John
lName  : Doe
email  : john.doe@email.com
alive  : true
=hashCode=: 686393765