XStatic

XStatic is a PHP library for enabling static proxy interfaces—similar to Laravel 4 "Facades"—but with any PHP project. XStatic was created by Jeremy Lindblom.

Introduction (Q&A)

Facades? Static Proxies? Isn't using static methods considered a bad practice?

Using static methods and classes makes your code harder to test. This is because your code becomes tightly coupled to the class being referenced statically, and mocking static methods for unit tests is difficult. For this and other reasons, using static methods is generally discouraged by object-oriented programming (OOP) experts. Generally, techniques involving design patterns like Service Locator and Dependency Injection (DI) are preferred for managing object dependencies and composition.

But... using static methods is really easy.

True, and PHP developers that prefer frameworks like CodeIgniter, Laravel, Kohana, and FuelPHP are very accustomed to using static methods in their application development. In some cases, it is an encouraged practice among these communities, who argue that it makes the code more readable and contributes to Rapid Application Development (RAD).

So, is there any kind of compromise?

Yep! Laravel 4 has a concept called "facades" (Note: This is not the same as the Facade design pattern). These act as a static interface, or proxy, to an actual object instance stored in a service container. The static proxy is linked to the container using a few tricks, including defining class aliases via PHP's class_alias() function, and the use of the magic __callStatic() method. We can thank Taylor Otwell for developing this technique.

OK, then what is the point of XStatic?

XStatic uses the same technique as Laravel's "facades" system, but provides two additional, but important, features:

It works with any framework's service container - XStatic relies on the ContainerInterface of the container-interop project. You can use the Acclimate library to adapt any third-party containers to the normalized container interface that XStatic depends on.
It works within any namespace - XStatic injects an autoloader onto the stack, so no matter what namespace or scope you try to reference your aliased static proxy from, it will pass through the XStatic autoloader. You can configure XStatic to create the aliases in the global namespace, the current namespace, or a specific namespace.

Oh, and why is it called XStatic?

Two reasons:

It removes the static-ness of making static method invocations, since the method calls are proxied to actual object instances. Potential tagline: "Static interfaces without the static pitfalls".
It is pronounced like the word "ecstatic", because it is meant to provide developers (some of them at least) with a sense of joy.

Usage

To show you how to use XStatic, I will show you a simple Silex application.

Your application bootstrap:

<?php

// Include the Composer autoloader, of course
require 'vendor/autoload.php';

use Acclimate\Container\ContainerAcclimator;
use XStatic\ProxyManager;
use Silex\Application;
use Silex\Provider\TwigServiceProvider;

// Setup your Silex app/container
$app = new Application;
$app->register(new TwigServiceProvider, array(
    'twig.path' => __DIR__ . '/templates',
));
$app['db'] = function () {
    return new PDO('mysql:dbname=testdb;host=127.0.0.1', 'dbuser', 'dbpass');
};
$app->get('/', 'MyApp\Controller\Home::index'); // Routes "/" to a controller object

// Setup and enable XStatic
$acclimator = new ContainerAcclimator();
$proxyManager = new ProxyManager($acclimator->acclimate($app));
$proxyManager->addProxy('View', 'MyApp\Proxy\Twig');
$proxyManager->addProxy('DB', 'MyApp\Proxy\Pdo');
$proxyManager->enable(ProxyManager::ROOT_NAMESPACE_ANY);

// Run the app
$app->run();

Your Static Proxy classes:

namespace MyApp\Proxy
{
    use XStatic\StaticProxy;

    class Pdo extends StaticProxy
    {
        public function getInstanceIdentifier()
        {
            return 'db';
        }
    }

    class Twig extends StaticProxy
    {
        public function getInstanceIdentifier()
        {
            return 'twig';
        }
    }
}

Your controller class:

namespace MyApp\Controller;

class Home
{
    public function index()
    {
        // It just works!
        View::render('home.index', array(
            'articles' => DB::query('SELECT * FROM articles')
        );
    }
}

Pretty cool, huh? Some interesting things to note about this example is that we've actually hidden the fact that we are using PDO and Twig from the controller. We could easily swap something else in that uses the same interfaces, and the controller code would not need to be altered. All we would need to do is put different objects into the application container. In fact, that is exactly how testing the controller would work. The test could be bootstrapped with mock or stub objects put into the container.

Static interfaces without the static pitfalls.

XStatic Concepts

Static Proxy – Static class that proxies static method calls to instance methods on its Proxy Subject.
Proxy Subject (Instance) – An object instance, stored in a Container, that is linked to a Static Proxy.
Proxy Manager – Mediating object used to associate Static Proxies to an Alias Loader and Container.
Alias – A memorable class name used as an alias to a fully-qualified class name of a Static Proxy class.
Alias Loader – Maintainer of the associations between Aliases and Static Proxies. It is injected into the autoloader stack to handle Aliases as they are referenced.
Container – A IoC container (e.g., a Service Locator or DIC) that provides the Proxy Subject instances. It must implement the container-interop project's ContainerInterface.
Instance Identifier – An identifier used to fetch a Proxy Subject from a Container. Each Static Proxy must specify the Instance Identifier needed to get its Proxy Subject.
Root Namespace – The namespace that an Alias can be referenced in. This can be configured as the global namespace (default), a specific namespace, or any namespace (i.e., the Alias works from any namespace).

How it works

The following diagram shows what happens when a Static Proxy is referenced, assuming it was previously added to the Proxy Manager.

Inspiration

This library is heavily inspired by the Facades system in the Laravel 4 Framework.

Disclaimer

I would not consider myself to be for or against the use of static proxy interfaces (or Laravel's "Facades"), but I do think it is a fascinating and unique idea, and that it is very cool that you can write code this way and still have it work and be testable. I am curious to see if developers, especially library and framework developers, find ways to use, but not require, these static proxy interfaces in order to make their projects appeal to a wider range of PHP developers.