在Dart中打开类类型

Question

I'm looking to write a function in a Dart superclass that takes different actions depending on which subclass is actually using it. Something like this:

class Foo {
  Foo getAnother(Foo foo) {
    var fooType = //some code here to extract fooType from foo;
    switch (fooType) {
      case //something about bar here:
        return new Bar();
      case //something about baz here:
        return new Baz();
    }
  }
}

class Bar extends Foo {}

class Baz extends Foo {}

where the idea is that I have some object and want to get a new object of the same (sub)class.

The main question is what type should fooType be? My first thought was Symbol, which leads to easy case statements like case #Bar: , but I don't know how I would populate fooType with a Symbol. The only options I can think of are to do something like Symbol fooType = new Symbol(foo.runtimeType.toString()); but my understanding is that runtimeType.toString() won't work when converted to javascript. You could get around that by using Mirrors, but this is meant to be a lightweight library, so those aren't on the table. Object.runtimeType returns something of the Type class, but I have no idea how to create instances of Type I could use for the case statements. Maybe I'm missing some other piece of the Dart library that is better suited for this?

Answer 1

You can use the runtimeType in switch :

class Foo {
  Foo getAnother(Foo foo) {
    switch (foo.runtimeType) {
      case Bar:
        return new Bar();
      case Baz:
        return new Baz();
    }
    return null;
  }
}

In the case statements the class name is use directly (aka. class literal ). This gives a Type object corresponding to the class mentionned. Thus foo.runtimeType can be compared with the specified type.

Note that you can not use generics for now in class literals . Thus case List<int>: is not allowed.