如何在Dart 2中克隆（复制值）复杂对象

问题描述

我想使用Dart 2克隆一个复杂的对象（复制值），而不是引用。

I would like to clone a complex object (copy values), not referencing, using Dart 2.

示例：

class Person {
  String name;
  String surname;
  City city;
}

class City {
  String name;
  String state;
}

main List<String> args {
  City c1 = new City()..name = 'Blum'..state = 'SC';
  Person p1 = new Person()..name = 'John'..surname = 'Xuebl'..city = c1;


  Person p2 = // HERE, to clone/copy values... Something similar to p1.clone();
}

这样做的最佳方式是什么？

What would be the way (best practice) to do this?

更新说明：：此这里的重点是了解进行了许多改进的Dart 2是否具有复制复杂对象的功能。

Update note: This How can I clone an Object (deep copy) in Dart? was posted some time ago. The focus here is to understand if Dart 2 that is bringing many improvements, has a facility for copying complex objects.

推荐答案

您在这里向我们展示的课程，没有什么比

With the classes you have shown us here, there is nothing shorter than

Person p2 = Person()
  ..name = p1.name
  ..surname = p1.surname
  ..city = (City()..name = p1.city.name..state = p1.city.state);

如果您将 clone 方法添加到人和城市，那么您显然可以使用它。
该语言没有内置功能可让您复制对象的状态。

If you add a clone method to Person and City, then you can obviously use that.There is nothing built in to the language to allow you to copy the state of an object.

我建议更改类，至少要添加一个构造函数：

I would recommend changing the classes, at least by adding a constructor:

class Person {
  String name;
  String surname;
  City city;
  Person(this.name, this.surname, this.city);
}
class City {
  String name;
  String state;
  City(this.name, this.state);
}

然后您可以通过以下方式克隆：

Then you can clone by just writing:

Person P2 = Person(p1.name, p1.surname, City(p1.city.name, p1.city.state));

（还有）

我说有没有语言功能可以复制对象，但是实际上，如果您可以访问 dart：isolate 库，则可以：通过隔离通信端口发送对象。我不建议您使用该功能，但这是出于完整性考虑：

I say that there is no language feature to copy objects, but there actually is, if you have access to the dart:isolate library: Sending the object over a isolate communication port. I cannot recommend using that feature, but it's here for completeness:

import "dart:isolate";
Future<T> clone<T>(T object) {
  var c = Completer<T>();
  var port = RawReceivePort();
  port.handler = (Object o) {
    port.close();
    c.complete(o);
  }
  return c.future;
}

同样，我不建议使用这种方法。
它适用于像这样的简单对象，但不适用于所有对象（并非所有对象都可以通过通信端口发送，例如，一等函数或任何包含一等函数的对象）。

Again, I cannot recommend using this approach.It would work for simple objects like this, but it doesn't work for all objects (not all objects can be sent over a communication port, e.g., first-class functions or any object containing a first class function).

编写类以支持所需的操作，包括复制。

Write your classes to support the operations you need on them, that includes copying.

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