Declaring a new static variable outside of Class

Is there a way declaring new static variables outside of that class even if it's not set in class?

// Using this class as a static object.
Class someclass {
    // There is no definition for static variables.
}

// This can be initialized
Class classA {
    public function __construct开发者_Python百科() {
        // Some codes goes here
    }
}

/* Declaration */
// Notice that there is no static declaration for $classA in someclass
$class = 'classA'
someclass::$$class = new $class();

How can it be done?

Thank you for your advices.

This can't be done, because static variables, well... are STATIC and therefore cannot be declared dynamically.

EDIT: You might want to try using a registry.

class Registry {

    /**
     * 
     * Array of instances
     * @var array
     */
    private static $instances = array();

    /**
     * 
     * Returns an instance of a given class.
     * @param string $class_name
     */
    public static function getInstance($class_name) {
        if(!isset(self::$instances[$class_name])) {
            self::$instances[$class_name] = new $class_name;
        }

        return self::$instances[$class_name];
    }

}

Registry::getInstance('YourClass');

__get() magic method in PHP is called when you access non-existent property of an object.

You may have a container within which you'll handle this.

Edit:

See this:

Magic __get getter for static properties in PHP