Mirror
- Dart course
- Advanced
- Lesson 20/83
- 5 min
Learn InstanceMirror and ClassMirror.
InstanceMirror and ClassMirror
In dart:mirrors, reflect(obj) returns an InstanceMirror. Through this mirror you access the object's fields and methods.
reflectClass(T) returns a ClassMirror. A ClassMirror lets you list the class's fields, methods and supertypes.
Example: var m = reflect(u); print(m.type.simpleName);. simpleName is a Symbol; convert it to text with MirrorSystem.getName(sym).
Symbol and getName
In the Mirror API, names are represented as Symbols. They are created with Symbol('name') or the #name literal.
To convert a Symbol to text, call MirrorSystem.getName(symbol). Example: MirrorSystem.getName(#hello) → 'hello'.
Symbols survive minification; therefore fields accessed via reflection are kept as Symbols.
Practice Inspect class fields via runtimeType
Define class Point { double x; double y; Point(this.x, this.y); }. Inside main create var p = Point(3.0, 4.0);; add print(p.runtimeType); and print(p.x);.
Starter code
void main() {
// define the Point class (outside main)
// create an instance; print runtimeType and x
}Sample solution
class Point {
double x;
double y;
Point(this.x, this.y);
}
void main() {
var p = Point(3.0, 4.0);
print(p.runtimeType);
print(p.x);
}Expected output
Point 3.0
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Reflect an object
var m = ____(u);var m = reflect(u);Explanation: reflect(u) returns an InstanceMirror.
2 What does reflectClass return?
- Symbol
- InstanceMirror
- Type
- ClassMirror Correct answer
Explanation: reflectClass returns a ClassMirror.
3 Match mirror concepts
| Term | Meaning |
|---|---|
reflect(obj) |
InstanceMirror |
reflectClass(T) |
ClassMirror |
Symbol |
Name abstraction |
getName |
To-text conversion |