Metadata

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

Two annotations are available to all Dart code: @deprecated and@override. For examples of using @override,see Extending a class.Here’s an example of using the @deprecatedannotation:

  1. class Television {
  2.   /// _Deprecated: Use [turnOn] instead._
  3.   @deprecated
  4.   void activate() {
  5.     turnOn();
  6.   }
  7.  
  8.   /// Turns the TV's power on.
  9.   void turnOn() {...}
  10. }

You can define your own metadata annotations. Here’s an example ofdefining a @todo annotation that takes two arguments:

  1. library todo;
  3. class Todo {
  4.   final String who;
  5.   final String what;
  7.   const Todo(this.who, this.what);
  8. }

And here’s an example of using that @todo annotation:

  1. import 'todo.dart';
  3. @Todo('seth', 'make this do something')
  4. void doSomething() {
  5.   print('do something');
  6. }

Metadata can appear before a library, class, typedef, type parameter,constructor, factory, function, field, parameter, or variabledeclaration and before an import or export directive. You canretrieve metadata at runtime using reflection.