Extension Methods trong Dart

extension StringExtension on String {
  String get reversed => split('').reversed.join();
  bool get isEmail => contains('@') && contains('.');
  String capitalize() => 
      isEmpty ? this : '${this[0].toUpperCase()}${substring(1)}';
}
 
print("hello".reversed);     // olleh
print("[email protected]".isEmail);  // true
print("dart".capitalize());  // Dart

extension ListExtension<T> on List<T> {
  T? get secondOrNull => length > 1 ? this[1] : null;
}
 
var list = [1, 2, 3];
print(list.secondOrNull);  // 2

extension BuildContextExtension on BuildContext {
  double get screenWidth => MediaQuery.of(this).size.width;
  void showSnackBar(String message) {
    ScaffoldMessenger.of(this).showSnackBar(
      SnackBar(content: Text(message)),
    );
  }
}
 
// Usage
context.showSnackBar("Hello!");