Metadata

Use metadata to give additional information about your code. A metadata annotation begins with the character @, followed by either a reference to a compile-time constant (such as deprecated) or a call to a constant constructor.

Four annotations are available to all Dart code: @Deprecated, @deprecated, @override, and @pragma. For examples of using @override, see Extending a class. Here's an example of using the @Deprecated annotation:

class Television {
  /// Use [turnOn] to turn the power on instead.
  @Deprecated('Use turnOn instead')
  void activate() {
    turnOn();
  }

  /// Turns the TV's power on.
  void turnOn() {...}
  // ···
}

You can use @deprecated if you don't want to specify a message. However, we recommend always specifying a message with @Deprecated.

You can define your own metadata annotations. Here's an example of defining a @Todo annotation that takes two arguments:

class Todo {
  final String who;
  final String what;

  const Todo(this.who, this.what);
}

And here's an example of using that @Todo annotation:

@Todo('Dash', 'Implement this function')
void doSomething() {
  print('Do something');
}

Metadata can appear before a library, class, typedef, type parameter, constructor, factory, function, field, parameter, or variable declaration and before an import or export directive.

Unless stated otherwise, the documentation on this site reflects Dart 3.6.0. Page last updated on 2024-11-17. View source or report an issue.