Use with Private Variables

Use with Private Variables

About

• Encapsulation: Hide implementation
• Controlled Access: Validate changes
• API Stability: Change internals safely
• Naming Convention: _ prefix

Main Topics

1. Basic Encapsulation

   • Definition: Private fields with public accessors

   • Example:

     class Wallet {
       double _balance = 0;
     
       double get balance => _balance;
     }

2. Validation

   • Definition: Protect invariants
   • Example:

     set balance(double value) {
       if (value < 0) throw ArgumentError();
       _balance = value;
     }

3. Read-only Exposure

   • Definition: Public getter, private setter

   • Example:

     class Circle {
       final double _radius;
     
       double get radius => _radius;
     }

4. Derived State

   • Definition: Computed from private fields
   • Example:

     get area => pi * _radius * _radius;

5. Change Notification

   • Definition: Trigger actions on change
   • Example:

     set value(int v) {
       _value = v;
       _notifyListeners();
     }

How to Use

• Data Hiding: Keep fields private
• Validation: In setters
• Computed Values: Via getters
• Documentation: Explain public API

How It Works

1. Privacy: _ prefix limits scope
2. Access: Getters/setters control visibility
3. Maintenance: Internal changes don’t break API
4. Tooling: Analyzer enforces access

Example:

class User {
  String _id;
  String _name;

  User(this._id, this._name);

  // Public API
  String get id => _id;
  String get name => _name;

  set name(String value) {
    if (value.isEmpty) throw ArgumentError();
    _name = value;
  }
}

Conclusion

Combining private variables with getters and setters provides robust encapsulation, allowing classes to maintain strict control over their internal state while exposing a clean, validated public API. This pattern is fundamental to object-oriented design in Dart.