Public and Private Members

Public and Private Members

About

• Public Members: Visible to all code (default)
• Private Members: Visible only within library (_ prefix)
• Applies to class fields, methods, top-level variables
• Essential for encapsulation

Main Topics

1. Public Access

   • Definition: Default visibility
   • Example:

     class User {
       String name; // Public by default
     }

2. Private Members

   • Definition: _ prefix convention
   • Example:

     class User {
       String _id; // Private to library
     }

3. Method Visibility

   • Definition: Applying to methods

   • Example:

     class Calculator {
       int _current = 0;
     
       void _reset() { // Private method
         _current = 0;
       }
     }

4. Top-level Privacy

   • Definition: Outside classes
   • Example:

     String publicVar = 'visible';
     String _privateVar = 'hidden';

5. Getter/Setter Control

   • Definition: Exposing private fields

   • Example:

     class Wallet {
       double _balance = 0;
     
       double get balance => _balance; // Public read-only
     }

How to Use

• Encapsulation: Hide implementation details
• API Design: Expose only what’s needed
• Naming: _ prefix for private members
• Testing: Use library structure for access

How It Works

1. Compilation: _ prefix triggers privacy
2. Scope: Library boundary enforcement
3. Visibility: Analyzer enforces access rules
4. Tooling: IDE shows visibility cues

Example:

class BankAccount {
  String _accountNumber; // Private
  double balance = 0;    // Public

  BankAccount(this._accountNumber);

  void _logTransaction() { // Private
    print('Transaction for $_accountNumber');
  }
}

Conclusion

Dart’s public/private access control through naming conventions provides a simple yet effective way to manage encapsulation. By prefixing members with _, developers can hide implementation details while exposing clean public APIs, leading to more maintainable code.