note 70025 added to language.oop5.patterns

cortex is right - it took me hours to figure it out. None
the less it's sometimes useful to let one sigleton class
extend another. You can achieve this by only using static
attributes:

<?php
  class A {
    private static $value = 0;
    private static $instance = null;
    
    private function __construct() {
      $this->set(time());
    }
    
    public static function getInstance() {
      if (is_null((self::$instance))) {
        $class_name = __CLASS__;
        self::$instance = new $class_name;
      } 
      
      return self::$instance;
    }
    
    private function set($i) {
      self::$value = $i;
      $this->out();
    }
    
    public function out() {
      echo self::$value;
    }
  }

  class B extends A {
    public static $instance = null;
    
    public static function getInstance() {
      parent::getInstance();
      if (is_null(self::$instance)) {
        $class = __CLASS__;
        self::$instance = new $class;
      }
      return self::$instance;
    }
  }

  $b = B::getInstance();
  $b->out();
?>

This will output the current time twice. If $value isn't
static, the call to $b->out() will output 0. Maybe it can
save someone some time...
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Manual Page -- http://www.php.net/manual/en/language.oop5.patterns.php
Edit        -- https://master
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Del: integrated  -- h
ttps://master.php.net/note/delete/70025/integrated
Del: useless     -- http
s://master.php.net/note/delete/70025/useless
Del: bad code    -- htt
ps://master.php.net/note/delete/70025/bad+code
Del: spam        -- https:/
/master.php.net/note/delete/70025/spam
Del: non-english -- 
https://master.php.net/note/delete/70025/non-english
Del: in docs     -- http
s://master.php.net/note/delete/70025/in+docs
Del: other reasons-- https://mast
er.php.net/note/delete/70025
Reject      -- https://mast
er.php.net/note/reject/70025
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