Reflection
- Dart course
- Advanced
- Lesson 19/83
- 5 min
Learn reflection with dart:mirrors.
What is reflection?
Reflection is a program inspecting its own structure at runtime: class names, fields, methods, annotations. In Dart the dart:mirrors library provides it.
Typical uses: serialization (JSON ↔ object), dependency injection, test mocks. But dart:mirrors is not supported in Flutter/AOT; most projects therefore prefer code generation (source_gen).
The simplest reflection tool is runtimeType: every object knows its type. obj.runtimeType returns the corresponding Type object.
Type info via runtimeType
Every Dart object has a runtimeType property. It returns the object's dynamic type and does not require mirrors — it works everywhere.
Example: var u = User('Ayşe'); print(u.runtimeType); prints User. This is the simplest form of reflection.
Deeper inspection (listing fields, dynamic method invocation) requires dart:mirrors; but runtimeType suffices for most debug and logging needs.
Practice Print the type with runtimeType
Define class User { String name; User(this.name); }. Inside main create var u = User('Ayşe'); and add print(u.runtimeType);.
Starter code
void main() {
// define the User class (outside main)
// create an instance and print its type name
}Sample solution
class User {
String name;
User(this.name);
}
void main() {
var u = User('Ayşe');
print(u.runtimeType);
}Expected output
User
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Where is dart:mirrors unsupported?
- Dart VM (console)
- Only web
- Flutter / AOT compilation Correct answer
- Test environment
Explanation: dart:mirrors does not work in Flutter and AOT compilation.
2 Get type info
print(u.____);print(u.runtimeType);Explanation: runtimeType gives the object's dynamic type.
3 Match reflection tools
| Term | Meaning |
|---|---|
dart:mirrors |
Full reflection |
runtimeType |
Basic type info |
source_gen |
Code generation |
annotation |
Metadata |