Factory Constructors

Factory Constructors

About

  • Factories control instance creation.
  • Can return existing instances.
  • Implement design patterns.
  • More flexible than generative constructors.

Main Topics

  1. Basic Factory

    • **Definition: factory` keyword.
    • Example: 
      class Logger {
  factory Logger() => _instance ??= Logger._internal();
}

  2. Object Pooling

    • **Definition`: Reusing instances.
    • Example: 
      factory Connection.fromPool() {...}

  3. Cache Patterns

    • **Definition`: Returning cached copies.
    • Example: 
      factory Config.load() => _cache ??= _loadConfig();

  4. Subtype Return

    • **Definition`: Return different types.
    • Example: 
      factory Shape.fromType(String type) {
  return type == 'circle' ? Circle() : Square();
}

How to Use

  • **Declare: Use factory` keyword
  • **Return`: Existing or new instances
  • **Cache`: Implement singleton patterns
  • **Flexibility`: Return subtypes

How It Works

  • No this: Doesn’t create new instance
  • **No Initializers: Can't use this`
  • **Flexible`: Can return anything

Example Session:

void main() {
  var logger = Logger(); // Returns singleton
  var shape = Shape.fromType('circle'); // Returns Circle
}

Conclusion

Factory constructors provide controlled object creation points, enabling sophisticated instantiation patterns while maintaining a clean public API surface.