Dependency Injector

Dependency Injector

A dependency injector resolves the dependencies of your class and makes sure that the correct objects are injected when the class is instantiated.

There is only one injector that I can recommend: Auryn. Sadly all the alternatives that I am aware of are using the service locator antipattern in their documentation and examples.

Install the Auryn package and then create a new file called Dependencies.php in your src/ folder. In there add the following content:

<?php declare(strict_types = 1);

$injector = new \Auryn\Injector;

$injector->alias('Http\Request', 'Http\HttpRequest');
$injector->define('Http\HttpRequest', [
    ':get' => $_GET,
    ':post' => $_POST,
    ':cookies' => $_COOKIE,
    ':files' => $_FILES,
    ':server' => $_SERVER,

$injector->alias('Http\Response', 'Http\HttpResponse');

return $injector;

Make sure you understand what alias, share and define are doing before you continue. You can read about them in the Auryn documentation.

You are sharing the HTTP objects because there would not be much point in adding content to one object and then returning another one. So by sharing it you always get the same instance.

The alias allows you to type hint the interface instead of the class name. This makes it easy to switch the implementation without having to go back and edit all your classes that use the old implementation.

Of course your Bootstrap.php will also need to be changed. Before you were setting up $request and $response with new calls. Switch that to the injector now so that we are using the same instance of those objects everywhere.

$injector = include('Dependencies.php');

$request = $injector->make('Http\HttpRequest');
$response = $injector->make('Http\HttpResponse');

The other part that has to be changed is the dispatching of the route. Before you had the following code:

$class = new $className($response);

Change that to the following:

$class = $injector->make($className);

Now all your controller constructor dependencies will be automatically resolved with Auryn.

Go back to your Homepage controller and change it to the following:

<?php declare(strict_types = 1);

namespace Example\Controllers;

use Http\Request;
use Http\Response;

class Homepage
    private $request;
    private $response;

    public function __construct(Request $request, Response $response)
        $this->request = $request;
        $this->response = $response;

    public function show()
        $content = '<h1>Hello World</h1>';
        $content .= 'Hello ' . $this->request->getParameter('name', 'stranger');

As you can see now the class has two dependencies. Try to access the page with a GET parameter like this http://localhost:8000/?name=Arthur%20Dent.

Congratulations, you have now successfully laid the groundwork for your application.