Storage class, dependency injection and singletons

Question

In re-writing my PHP framework vervPHP, I've created the following class:

class storage {
    private static $instance;
    public $db = null; // Holds a database connection object
    public $user = null; // Holds user related information for custom auth
    public $data = array(); // Array of data for storage

    private function __construct(){
        // Create the default array in $this->data....
    }

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

    // Getters, Setters and other stuff follows...
}

When my framework starts up, it looks like this:

index.php:

// Kick it off!
verv\init();

framework/verv/verv.php:

function init() {
    $verv = storage::singleton();

    loadConfig($verv);
    loadRequest($verv);
    connectDB($verv);
    authenticateUser($verv);
    loadModule($verv);
    loadTemplate($verv);
    renderPage($verv);
}

$verv is passed by reference - so any changes are saved as it moves around.

My question is, do I need the singleton portion? And basically, am I doing it "right"? The code in question works (albeit it needs a little tidying) but I want to make sure that my storage class is as robust and efficient as possible.

Answer 1

Read this post before using the singleton pattern: https://stackoverflow.com/a/4596323/1908639

You might find that it increases your initial development speed; however, the downsides tend to increase with the size/complexity of the project. I have personally maintained code that used singletons, and I found it difficult to test/reuse.

If you think there are any major advantages to the singleton approach, I would be interested in hearing them. I have not been able to find any beneficial use-cases in PHP web development, but I am definitely interested in hearing about them, if they exist.

Also, passing objects by reference should not be necessary in PHP 5 (source):

In PHP 5 there is a new Object Model. PHP's handling of objects has been completely rewritten, allowing for better performance and more features. In previous versions of PHP, objects were handled like primitive types (for instance integers and strings). The drawback of this method was that semantically the whole object was copied when a variable was assigned, or passed as a parameter to a method. In the new approach, objects are referenced by handle, and not by value (one can think of a handle as an object's identifier).

Answer 2

I think you are going to the wrong direction with this kind of aproach. First you are creating a Singleton while propably you don't need to use it. Second you are mixing things in one God object which is also a bad design in an object-oriented environment. And what is this init() function? Just laying around in a namespace alone in the dark? Bad design. Most beginner PHP programmers are don't know that passing by reference things are can really hurt performance and BTW objects are passed by not reference but an internal handler which will give you the possibility to modify (not unset or overwrite) that object.

Answer 3

Because you are passing things in via dependency injection, it does render the singleton a bit pointless in the code you have shown. Normally, it is useful in that you can call the storage::singleton() method from anywhere and know that you will have the exact same object. However, this causes a problem because unit testing becomes difficult as you can't decouple the function from the singleton, so your code as it stands is far easier to test.

You do however have the advantage with the singleton that other people using your framework can't wreck it by ignoring the dependency injection and just making a new instance of the storage class somewhere, so actually I think this is a good approach.

I'm not quite sure why you have the page construction process contained within init() as you could really just have those raw function calls on the main index.php page. You appear to be already using a router pattern of some sort, so presumably index.php acts a single entry point anyway.