Summary - Metadata
- Dart course
- Intermediate
- Lesson 81/116
- 5 min
Combine annotations, @override and reflection to write an annotation processor.
Summary: Metadata
In this group you saw annotations, the @override and @deprecated tags, writing custom annotations and reflection with dart:mirrors. Annotations add metadata to code; @override catches wrong overrides.
Now we combine them: we will define a custom annotation and apply it to a method. This shows how annotations carry labels.
Remember: an annotation is a class with a const constructor; @override is recommended; @deprecated warns.
Practice The Review annotation
Define a Review annotation class with a final String note field and a const Review(this.note) constructor. Write a Report class with a @Review('important') void generate() { print('generated'); } method. In main call Report().generate().
Starter code
// Define the Review annotation class (note, const constructor)
// Define the Report class and the generate method
void main() {
// call the generate method
}Sample solution
class Review {
final String note;
const Review(this.note);
}
class Report {
@Review('important')
void generate() {
print('generated');
}
}
void main() {
Report().generate();
}Expected output
generated
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Concept matching
| Term | Meaning |
|---|---|
@override |
Override |
@deprecated |
Deprecated mark |
class Todo |
Custom annotation |
dart:mirrors |
Reflection |
2 What is a custom annotation made of?
- An enum
- A Future
- A class with a const constructor Correct answer
- An abstract method
Explanation: a custom annotation is a class with a const constructor.
3 Applying an annotation
@____('önemli')
void generate() {}@Review('önemli')
void generate() {}Explanation: the annotation is applied with @Review.