flutter - 如何从对象实例的类型实例化泛型？

Question

这是我的代码:

class Foo {}
class MyClass extends Foo {}
class HisClass extends Foo {}
class YourClass extends Foo {}

var x = [
  MyClass(),
  HisClass(),
  YourClass()
];

class Something<T extends Foo> {}

我想从 Something创建一个 x类的列表。我以为我应该可以这样做，但是会产生 'dynamic' doesn't extend 'Foo'. Try using a type that is or is a subclass of 'Foo'.darttype_argument_not_matching_bounds错误

List<Something> list = x.map((entry) => new Something<entry.runtimeType>())

如何使编译器对我所做的事情安全感到满意？

Answer 1

可能是这样的:

void main() async {
  var x = [MyClass(), HisClass(), YourClass()];

  var list = x.map(Something
      .builder); // Instance of 'Something<MyClass>', Instance of 'Something<HisClass>', Instance of 'Something<YourClass>'

  print(list);
}

class Foo {}

class MyClass extends Foo {}

class HisClass extends Foo {}

class YourClass extends Foo {}

class Something<T extends Foo> {
  Something();

  static Something<Foo> builder(Foo item) {
    switch (item.runtimeType) {
      case (MyClass):
        return Something<MyClass>();
      case (HisClass):
        return Something<HisClass>();
      case (YourClass):
        return Something<YourClass>();
    }

    return Something<Foo>();
  }
}