Constructors trong Dart

🎯 Mục tiêu: Các loại constructors trong Dart.

💡 Default Constructor


class Person {
  String name;
  int age;
  
  // Short syntax
  Person(this.name, this.age);
  
  // Full syntax
  // Person(String name, int age) {
  //   this.name = name;
  //   this.age = age;
  // }
}

📝 Named Constructor


class Point {
  double x, y;
  
  Point(this.x, this.y);
  
  Point.origin() : x = 0, y = 0;
  Point.fromJson(Map<String, double> json)
      : x = json['x']!,
        y = json['y']!;
}
 
var p1 = Point(10, 20);
var p2 = Point.origin();
var p3 = Point.fromJson({'x': 5, 'y': 10});

🔧 Const Constructor


class ImmutablePoint {
  final double x, y;
  
  const ImmutablePoint(this.x, this.y);
}
 
// Compile-time constant
const origin = ImmutablePoint(0, 0);

🎯 Factory Constructor


class Logger {
  static final Map<String, Logger> _cache = {};
  
  final String name;
  
  factory Logger(String name) {
    return _cache.putIfAbsent(name, () => Logger._internal(name));
  }
  
  Logger._internal(this.name);
}

✅ Checklist

this. shorthand
Named constructors
const constructors
factory cho singletons/caching