Summary - Metadata

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.

Exercise 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().

Show example solution

class Review {
  final String note;
  const Review(this.note);
}

class Report {
  @Review('important')
  void generate() {
    print('generated');
  }
}

void main() {
  Report().generate();
}

Test yourself

Concept matching

@override

Override
@deprecated

Deprecated mark
class Todo

Custom annotation
dart:mirrors

Reflection
What is a custom annotation made of?
- An enum
- A Future
- A class with a const constructor
- An abstract method
Show answer

A class with a const constructor — a custom annotation is a class with a const constructor.

Applying an annotation

@____('önemli')
void generate() {}

Show answer

@Review('önemli')
void generate() {}

Next lesson: dart test

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