# Replace getter and setter blocks with a oneliner when using ChangeNotifier.

When dart became ‘non-nullable by default’, an interesting keyword was added to the dart language: **‘late’**.

Although it might not be so obvious at first glance, this keyword makes it possible to simplify getter and setter blocks when using a ChangeNotifier to update values on the screen.

Normally a getter and setter block does look like this.

```
int _counter = 0;

int get counter => _counter;

set counter(int value) {
  if (_counter != value) {
    _counter = value;
    notifyListeners();
  }
}
```

This code is not complicated. It consists of:

*   a private backing variable
*   a public getter and setter
*   some logic that tests if the value has changed and calls ‘notifyListeners’ when needed

There are also some drawbacks:

*   You can access the backing variable directly (by accident).
*   It is easy to make mistakes like checking or assigning the wrong backing variable, especially when you have more than 3 pairs of getters and setters.
*   The code is boring (error-prone) and takes up too much space.
*   Don’t repeat yourself (DRY) principle is not respected.

Now with the ‘late’ keyword, we can replace the code above with this one-liner:

```
late final counter = Property(0, notifyListeners);
```

Without the ‘late’ keyword this would not have been possible, because it is not allowed to access member functions (in this case `notifyListeners`) in an initializer. With the late keyword, initialization is deferred until the property is first referenced.

The implementation of the Property class is simple and solves all drawbacks of a regular getter and setter block.

```
class Property<T> {
  Property(T initialValue, this.notifyListeners) {
    _value = initialValue;
  }

  late T _value;
  final void Function() notifyListeners;

  T get value => _value;

  set value(T value) {
    if (_value != value) {
      _value = value;
      notifyListeners();
    }
  }
}
```

This makes it possible to reduce the business logic of the default Flutter counter app to these few lines:

```
class MainController extends ChangeNotifier {
  late final counter = Property<int>(0, notifyListeners);

  void incrementCounter() => counter.value++;
}
```

%[https://codepen.io/jsroest/pen/poWKLaG]

Source code to test this out can be found here:  
[https://github.com/jsroest/property_for_changenotifier](https://github.com/jsroest/property_for_changenotifier)