Why were anonymous classes invented?

Anonymous classes allow creating a simple, one-time object of a class for use in a specific place without explicitly defining the class. This is useful in the following cases:

• Implementing interfaces or extending classes on the fly: Often, there is a need to create an object that simply implements an interface method or inherits functionality from a base class for one-time use.

  // Instead of
  // class MyListener implements EventListener { public function handle(Event $event) { /* ... */ } }
  // $emitter->on('event', new MyListener());
  
  // You can
  $emitter->on('event', new class implements EventListener {
      public function handle(Event $event) {
          // Event handling logic
          echo "Event processed!\n";
      }
  });
  

• Reducing code size: Eliminates the need to create a separate file for a small class used only in one place.
• Use in callbacks and closures: Convenient for passing an object with specific methods as a callback.

  function processData(array $data, object $processor) {
      foreach ($data as $item) {
          $processor->process($item);
      }
  }
  
  processData([1, 2, 3], new class {
      public function process($item) {
          echo "Processing item: " . $item . "\n";
      }
  });
  

• Testing: For creating mocks or stubs without defining full classes.
• Encapsulation: Allows combining data and behavior specific to a particular task without polluting the global namespace.

They are syntactic sugar to simplify code where a full class definition would be excessive.