Reflection

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.

Exercise 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);.

Show example solution

class User {
  String name;
  User(this.name);
}

void main() {
  var u = User('Ayşe');
  print(u.runtimeType);
}

Test yourself

Where is dart:mirrors unsupported?
- Dart VM (console)
- Only web
- Flutter / AOT compilation
- Test environment
Show answer

Flutter / AOT compilation — dart:mirrors does not work in Flutter and AOT compilation.
Get type info
```
print(u.____);
```
Show answer
```
print(u.runtimeType);
```
Match reflection tools

dart:mirrors

Full reflection
runtimeType

Basic type info
source_gen

Code generation
annotation

Metadata

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