Dart 中的通用 getter/setter？

Question

我需要一种通用的方法来访问对象的属性/getter。

在 JavaScript 中，这可以通过

const obj = {
    foo: 'Hello World',
    bar: 123
};

const propName = 'foo';
console.log(o[propName]); // "Hello World"

那么，如果我在 Dart 中有一个类，如下面的类，我将如何以通用方式访问属性？也许是运算符重载之类的？

class MyFooClass with ChangeNotifier {
  String _someText = 'Hello World';
  int _someNumber = 123;

  get someText => _someText;
  set someText(value) => _someText = value;

  get someNumber => _someNumber;
  set someNumber(value) => _someNumber = value;
}

var myFoo = MyFooClass();
print(myFoo['someText']); // The operator '[]' isn't defined for the class 'MyFooClass'

Answer 1

可以使用dart:mirrors（请注意，我删除了一些内容以使其自行编译）：

import 'dart:mirrors';

class MyFooClass {
  String _someText = 'Hello World';
  int _someNumber = 123;

  get someText => _someText;
  set someText(value) => _someText = value;

  get someNumber => _someNumber;
  set someNumber(value) => _someNumber = value;

  operator [](String name) {
    InstanceMirror i = reflect(this);

    for (DeclarationMirror declMirror in i.type.declarations.values) {
      if (declMirror.isPrivate) {
        continue;
      }

      Symbol simpleName = declMirror.simpleName;

      // It's not possible to get the name from a symbol directly: https://github.com/dart-lang/sdk/issues/28372
      if (simpleName.toString() == 'Symbol("${name}")') {
        return i.getField(simpleName).reflectee;
      }
    }
  }
}

像这样使用它：

void main() {
  var myFoo = MyFooClass();
  print(myFoo['someText']); // 'Hello, World!'
  print(myFoo['someNumber']); // 123
  print(myFoo['some non existent thing']); // null
}

---

旧答案

这是你想要的吗？

void main() {
  var o = {'foo': 'Hello World', 'bar': 123};
  var propName = 'foo';

  print(o[propName]); // 'Hello World'
}