what is the exact difference between PHP static class and singleton class

Question

I have always used a Singleton class for a registry object in PHP. As all Singleton classes I think the main method looks like this:

class registry
{
    public static function singleton()
    {
        if( !isset( self::$instance ) )
        {
            self::$instance = new registry();
        }
        return self::$instance;
    }

    public function doSomething()
    {
        echo 'something';
    }
}

So whenever I need something of the registry class I use a function like this:

registry::singleton()->doSomethine();

Now I do not understand what the difference is between creating just a normal static function. Will it create a new object if I just use a normal static class.

class registry
{
    public static function doSomething()
    {
        echo 'something';
    }
}

Now I can just use:

registry::doSomethine();

Can someone explain to me what the function is of the singleton class. I really do not understand this.

possible duplicate of [Difference between static class and singleton pattern?](http://stackoverflow.com/questions/519520/difference-between-static-class-and-singleton-pattern) — Sarfraz, May 17 '10 at 14:08

Simon · Accepted Answer · 2010-05-17T14:58:38.863

A static function is a function that can be called without creating an object of a class.

registry::doSomething()

A Singleton is a design pattern, that should prevent the users of the class from creating more than one instance of a class. So, there is usually only one instance of a singleton class. A Singleton's constructor should be declared private and have a static method providing a single instance-object:

class Singleton
{
   private Singleton()
   {
   }

   private static var $instance = null;

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

For more information see http://en.wikipedia.org/wiki/Singleton_pattern

P.S: Sorry for my bad PHP, the syntax may not be 100% correct, but you should roughly understand what I mean in terms of OOP.

score 1 · Answer 2 · answered May 17 '10 at 15:07

The fact that the Singleton is a design-pattern that restricts instantiation of a class to one single object, it is possible to do some stuff that is slightly more difficult with a static class:

Lazy initialization
Replace implementation internally by sub-classing the Factory
Manage via configuration

However, there are several drawbacks to singletons, so it is better in general to use patterns such as Factory as you get additional benefits such as decoupling.

what is the exact difference between PHP static class and singleton class

2 Answers2