Extension Methods

🎯 Mục tiêu: Thêm methods cho existing types.

---

💡 Cú pháp

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 cho generic types

extension ListExtension<T> on List<T> {
  T? get secondOrNull => length > 1 ? this[1] : null;
}

var list = [1, 2, 3];
print(list.secondOrNull);  // 2

---

📱 Trong Flutter

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!");

---

✅ Checklist

• extension Name on Type { }
• Thêm methods, getters, operators
• Generic extensions

---