创建单身人士 - 这是真的吗？

Question

I am trying to create my own sort of lightweight,yet OOP way to keep track of loaded files and their appropriate versions (not yet implemented) in my PHP framework to be able to easily test dependency issues in the future.

Here's my current code, but being a total newcomer to OOP and patterns I am not able to determine if I have accomplished a proper Singleton or not:

class loadRegistry {

    private static $registry = null;

    private function __construct(){

        if (is_null(self::$registry));
        self::$registry = array();

    }

    public static function get() {
        return self::$registry;
    }

    public static function set($filename){

        if ( isSet( self::$registry[$filename]) AND !empty($filename) ) {
            throw new Exception("File already loaded");
        }
        else self::$registry[$filename] = '';
    }

}

loadRegistry::set('filename');
loadRegistry::set('filename2');

$reg = loadRegistry::get();

Answer 1

No, it is not a singleton. You are actually only playing with static properties. A singleton would be more like this:

class Registry {

    private static $registry = null;
    private $data;

    private function __construct(){
        $this->data = array();
    }

    public static function getInstance() {
        if (is_null(self::$registry)) {
            self::$registry = new Registry();
        }
        return self::$registry;
    }

    public function set($filename){
        if (isset($this->data[$filename]) && !empty($filename) ) {
            throw new Exception("File already loaded");
        }
        else {
            $this->data[$filename] = '';
        }
    }

    // further **instance** methods
}

$reg = Registry::getInstance();
$reg->set('filename');
$reg->set('filename2');

I don't know whether you can set the constructor as private in PHP... I think not.

There is a difference between static classes^$ and a singleton. A singleton allows to have only one instance at a time. For static classes, you don't even need an instance. In addition, static properties are shared between all instances of the class (in case you create an instance).

You normally use static classes if you don't need an instance to hold some state.

$: There are no real static classes. Only members can be defined as static. I'd say a class that has only static members can be called a static class.