Generic getter/setter in Dart?

user_2375243 0
Viewed 1070

I need a generic way to access an object's property/getter.

In JavaScript this can be done via

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

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

So, if I had a class in Dart, like the one below, how would I access a property in a generic way? Maybe with operator overloading or something?

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'
dart generic-programming getter-setter
1 Answers

It's possible using dart:mirrors (note that I have removed a few things to make it compile on its own):

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;
      }
    }
  }
}

Use it like:

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

Old answer

Is this what you want?

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

  print(o[propName]); // 'Hello World'
}
user_23439350
Related