Quick Start

This quick start is intended to get developers familiar with the concepts of the zend-di DiC. Generally speaking, code is never as simple as it is inside this example, so working knowledge of the other sections of the manual is suggested.

Assume, for a moment, the following application code. It already assumes that dependencies are injected, and so becomes a good candiate for a DiC.

namespace MyLibrary
{
    class DbAdapter
    {
        protected $username = null;
        protected $password = null;

        public function __construct($username, $password)
        {
            $this->username = $username;
            $this->password = $password;
        }
    }
}

namespace MyMovieApp
{
    class MovieFinder
    {
        protected $dbAdapter = null;

        public function __construct(\MyLibrary\DbAdapter $dbAdapter)
        {
            $this->dbAdapter = $dbAdapter;
        }
    }

    class MovieLister
    {
        protected $movieFinder = null;

        public function __construct(MovieFinder $movieFinder)
        {
            $this->movieFinder = $movieFinder;
        }
    }
}

With the above code, you find yourself writing the following to wire and utilize it:

// $config object is assumed

$dbAdapter = new MyLibrary\DbAdapter($config->username, $config->password);
$movieFinder = new MyMovieApp\MovieFinder($dbAdapter);
$movieLister = new MyMovieApp\MovieLister($movieFinder);
foreach ($movieLister as $movie) {
    // iterate and display $movie
}

If you are doing this above wiring in each controller or view that wants to list movies, not only can this become repetitive and boring to write, but also unmaintainable if you want to swap out one of these dependencies on a wholesale scale.

Since this example of code already practices good dependency injection using constructor injection, it is a great candidate for using zend-di.

The following demonstrates how to wire the above into a zend-di container:

// Inside a bootstrap somewhere
$di = new Zend\Di\Di();
$di->instanceManager()->setParameters('MyLibrary\DbAdapter', [
    'username' => $config->username,
    'password' => $config->password,
]);

// Elsewhere:
$movieLister = $di->get('MyMovieApp\MovieLister');
foreach ($movieLister as $movie) {
    // iterate and display $movie
}

In the above example, we are obtaining a default instance of Zend\Di\Di. By 'default', we mean that Zend\\Di\\Di is constructed with a DefinitionList seeded with a RuntimeDefinition (which uses PHP's Reflection API) and an empty instance manager and no configuration:

public function __construct(
    DefinitionList $definitions = null,
    InstanceManager $instanceManager = null,
    Configuration $config = null
) {
    $this->definitions = ($definitions) ?: new DefinitionList(new Definition\RuntimeDefinition());
    $this->instanceManager = ($instanceManager) ?: new InstanceManager();

    if ($config) {
        $this->configure($config);
    }
}

This means that when $di->get() is called, it will be consulting the RuntimeDefinition, which uses Reflection to understand the structure of the code. Once it knows the structure of the code, it can then know how the dependencies fit together and how to go about wiring your objects for you. Zend\Di\Definition\RuntimeDefinition will utilize the names of the parameters in the methods as the class parameter names. This is how both the username and password keys are mapped to the first and second parameters, respectively, of the constructor consuming these named parameters.

If you were to want to pass in the username and password at call time, this is achieved by passing them as the second argument to get():

$di = new Zend\Di\Di();
$movieLister = $di->get('MyMovieApp\MovieLister', [
    'username' => $config->username,
    'password' => $config->password
]);
foreach ($movieLister as $movie) {
    // iterate and display $movie
}

It is important to note that when using call time parameters, these parameter names will be applied to any class that accepts a parameter of such name.

By calling $di->get(), this instance of MovieLister will be automatically shared. This means subsequent calls to get() will return the same instance as previous calls. If you wish to have completely new instances of MovieLister, you can utilize $di->newInstance().