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General questions about getting started with SilverStripe that don't fit in any of the categories above.

Moderators: martimiz, Sean, biapar, Willr, Ingo, swaiba, simon_w

static variables / singletons


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7 Posts   1861 Views

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richard-ward

Community Member, 31 Posts

3 September 2010 at 8:18am

Hi,

I'm struggling to create a singleton (i.e. following the proper design pattern for a singleton). My singleton is as follows:

class PlannerService {
   private $my_variable;
   private $my_other_variable;

   private static $instance;

   private function __construct() {
      $this->my_variable = time();
      $this->my_variable = time();
   }

   public static function getInstance() {
      if ($instance == null) {
         $instance = new PlannerService();
      }
      return $instance;
   }

   public function getMyVariable() {
      return $this->my_variable;
   }

   public function getMyOtherVariable() {
      return $this->my_other_variable;
   }
}

When i then call this from my controller as below, every time i call it, it thinks that $instance is null and creates a new object.

$instance = PlannerService::getInstance();
$instance->getMyVariable();

Any ideas?

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richard-ward

Community Member, 31 Posts

3 September 2010 at 7:52pm

I'm assuming this is possible btw!

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Mad_Clog

Community Member, 78 Posts

3 September 2010 at 7:59pm

Edited: 03/09/2010 8:00pm

Replace $instance with self::$instance in your getInstance method

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richard-ward

Community Member, 31 Posts

3 September 2010 at 8:35pm

Unfortunately that has not resolved the issue - i've replaced the getInstance method as below, but self::$instance == still returns true every time

   public static function getInstance() {
      if (self::$instance == null) {
         self::$instance = new PlannerService();
      }
      return self::$instance;
   }

Avatar
Mad_Clog

Community Member, 78 Posts

3 September 2010 at 9:00pm

You do realize the static variable is set on a per request basis.
In other words, every time you do a new request the variable will be empty initially, and set only after you first call the getInstance method.

How are you testing this code?
Because the new code does indeed use the singleton pattern.

Avatar
richard-ward

Community Member, 31 Posts

3 September 2010 at 9:07pm

Oh right, so statics do not exist across requests (sorry - i'm a Java developer, so I was hoping static meant the same thing as when working with that!). I'll find a different way to do what I need. Thanks!

Avatar
Mad_Clog

Community Member, 78 Posts

3 September 2010 at 9:15pm

Have a look here to learn more about statics:
http://nl3.php.net/manual/en/language.oop5.static.php