POC Singleton And Abstraction

PocSingletonAndAbstraction.php

<?php
/**
 * 
 * Proof Of Concept in PHP.
 * 
 * - Create a singleton class which is abstract, with abstract methods.
 * - Abstract methods are implemented by other classes, with as many implementations as desired.
 * 
 * 
 * @author chris-scientist
 * @version 1.0
 * 
 */

class BreakLine {
   public static $VALUE = "<br/>";
   
    private function __constructor() {}
}
 
abstract class AbstractSingleton {
   private static $DEFAULT_CLASS = 0;
    private static $OTHER_CLASS = 1;
 
   private static $instance = null;
    private static $type = 0;
   
   protected function __construct() {
           echo ("parent constructor" . BreakLine::$VALUE);
   }
  
   public static function forceOtherClass() {
           AbstractSingleton::$type = AbstractSingleton::$OTHER_CLASS;
   }
  
   public static function getInstance() {
       if(
           AbstractSingleton::$DEFAULT_CLASS == AbstractSingleton::$type &&
        (
          (
          AbstractSingleton::$instance === null
          ) ||
          (
          ! is_a(AbstractSingleton::$instance, "DefaultSingleton")
          )
        )
    ) {
           AbstractSingleton::$instance = new DefaultSingleton();
    } else if(
           AbstractSingleton::$OTHER_CLASS == AbstractSingleton::$type &&
        (
          (
          AbstractSingleton::$instance === null
          ) ||
          (
          ! is_a(AbstractSingleton::$instance, "OtherSingleton")
          )
        )
    ) {
           AbstractSingleton::$instance = new OtherSingleton();
    }
    return AbstractSingleton::$instance;
   }
  
   protected abstract function overrideFct();
  
   public function run() {
           $this->overrideFct();
   }
}
 
class DefaultSingleton extends AbstractSingleton {
          
    protected function __construct() {
           parent::__construct();
        echo ("default constructor" . BreakLine::$VALUE);
    }
   
    protected function overrideFct() {
           echo ("default process" . BreakLine::$VALUE);
    }
   
}
 
class OtherSingleton extends AbstractSingleton {
          
    protected function __construct() {
           parent::__construct();
        echo ("other constructor" . BreakLine::$VALUE);
    }
   
    protected function overrideFct() {
           echo ("other process" . BreakLine::$VALUE);
    }
   
}
 
// ======================================================
//
// Test
AbstractSingleton::getInstance()->run();
 
echo (BreakLine::$VALUE . BreakLine::$VALUE);
 
AbstractSingleton::forceOtherClass();
 
AbstractSingleton::getInstance()->run();

?>