Các phương thức mở rộng (Extension) trong Dart

abstract final class String implements Comparable<String>, Pattern {
   ...
}

extension MyStringExtension on String {

  String sayHello()  {
      return "Hello $this";
  }

  String sayBye()  {
    return "Bye $this";
  }
}

import 'my_string_extension.dart';

void main()  {
   // This is a String:
   String name = "Tom";

   var s1 = name.sayHello();
   print("s1 = $s1");

   var s2 = name.sayBye();
   print("s2 = $s2");
}

class Person {
  String name;
  String? phone;
  Person(this.name, this.phone);

  void intro() {
    print("Hi!, my name is $name");
  }
}

import 'person.dart';

extension PersonExtension on Person {
  void selfIntroduce() {
    print("Hello, my name is $name");
  } 
}

import 'person.dart';
import 'person_extension_1.dart';

void main() {
  var tom = Person("Tom", "123456789");

  tom.intro();
  tom.selfIntroduce();
}

// No name extension:
extension on String {
  String imagePath() {
    return "/static/images/$this";
  }
}

final String logoPath = "logo.png".imagePath();
final String carPath = "car.jpg".imagePath();

void main() {
  print("logoPath: $logoPath");
  print("carPath: $carPath");

  var buyNowPath = "buyNow.gif".imagePath();
  print("buyNowPath: $buyNowPath");
}