The Singleton Design Pattern for PHP

By Tony Marston
2005-07-29


A separate Helper method within each class

This method requires the addition of a getInstance() (or similar) method within each each and every class, similar to the following:

    function getInstance ()

    // this implements the 'singleton' design pattern.

    {

        static $instance;

        

        if (!isset($instance)) {

            $c = __CLASS__;

            $instance = new $c;

        } // if

        

        return $instance;

        

    } // getInstance

It is referenced with code similar to the following:

    require_once 'std.datevalidation.class.inc';

    $dateobj = DateClass::getInstance();

This method has the following advantages:

• It provides a consistent method across all classes.

This method has the following disadvantages:

• It requires that the class definition be pre-loaded.
• It must be defined within each and every (sub)class where it will be needed. Due to the way that it works it cannot be inherited from a superclass because a static method in a superclass does not know of the existence of any subclasses therefore cannot be used to instantiate a subclass.

Tutorial Pages:
» Introduction
» A non-class Helper function
» A separate Helper method within each class
» A single Helper method for all classes
» References
» Conclusion

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