const constructor
- Flutter course
- Beginner
- Lesson 19/99
- 4 min
Learn how const constructor improves performance.
const constructor
Marking a constructor const lets Flutter merge all instances created with the same parameters into a single canonical object. This reduces memory use and speeds up widget tree comparison. Using const where possible is a core Flutter performance tip.
class Etiket extends StatelessWidget {
final String metin;
const Etiket({super.key, required this.metin});
@override
Widget build(BuildContext context) {
return Text(metin);
}
}
// Usage:
Etiket(metin: 'Selam') // new object every time
const Etiket(metin: 'Selam') // single object, reusedCanonical instance
Objects produced with const are canonical: all instances made with the same values live at the same memory address. When comparing the widget tree, Flutter can tell whether two const widgets are identical with a single address comparison. This greatly speeds up the diff algorithm.
// non-const widget: each is a new object
Text('a')
Text('a')
// const widget: single object
const Text('a')
const Text('a')Practice Print const info
In main, print two lines with print: const tek nesne and canonical hizli.
Starter code
void main() {
// iki satır yazdır:
// const tek nesne
// canonical hizli
}Sample solution
void main() {
print('const tek nesne');
print('canonical hizli');
}Expected output
const tek nesne canonical hizli
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does a const constructor provide?
- Produces a new object each time
- Produces a single canonical object for same params Correct answer
- Allows changing parameters at runtime
- Makes the widget invisible
Explanation: A const constructor merges all instances made with the same params into a single canonical object.
2 const constructor call
final etiket = ____ Etiket(metin: 'Selam');final etiket = const Etiket(metin: 'Selam');Explanation: A constructor called with const produces a compile-time constant.
3 const constructor concepts
| Term | Meaning |
|---|---|
const |
Produces a compile-time constant |
canonical |
Single instance of the same object |
performance |
Less memory, faster diff |
const Etiket(...) |
Single object, reused |