Service Container

• Introduction
• Basic Usage
• Binding Interfaces To Implementations
• Contextual Binding
• Tagging
• Container Events

Introduction

Lumen utilizes the powerful Laravel service container, which is an amazing tool for managing class dependencies. Dependency injection is a fancy word that essentially means this: class dependencies are "injected" into the class via the constructor or, in some cases, "setter" methods.

Basic Usage

Note: To better organize your container bindings, consider placing them in service providers.

Registering A Basic Resolver

There are several ways the service container can register dependencies, including Closure callbacks and binding interfaces to implementations. First, we'll explore Closure callbacks. A Closure resolver is registered in the container with a key (typically the class name) and a Closure that returns some value:

$app->bind('FooBar', function($app) {
	return new FooBar($app['SomethingElse']);
});

Registering A Singleton

Sometimes, you may wish to bind something into the container that should only be resolved once, and the same instance should be returned on subsequent calls into the container:

$app->singleton('FooBar', function($app) {
	return new FooBar($app['SomethingElse']);
});

Binding An Existing Instance Into The Container

You may also bind an existing object instance into the container using the instance method. The given instance will always be returned on subsequent calls into the container:

$fooBar = new FooBar(new SomethingElse);

$app->instance('FooBar', $fooBar);

Resolving

There are several ways to resolve something out of the container. First, you may use the make method:

$fooBar = $app->make('FooBar');

Automatic Resolution

Secondly, but importantly, you may simply "type-hint" the dependency in the constructor of a class that is resolved by the container, including controllers, event listeners, queue jobs, and more. The container will automatically inject the dependencies:

<?php namespace App\Http\Controllers;

use App\Http\Controllers\Controller;
use App\Users\Repository as UserRepository;

class UserController extends Controller {

	/**
	 * The user repository instance.
	 */
	protected $users;

	/**
	 * Create a new controller instance.
	 *
	 * @param  UserRepository  $users
	 * @return void
	 */
	public function __construct(UserRepository $users)
	{
		$this->users = $users;
	}

	/**
	 * Show the user with the given ID.
	 *
	 * @param  int  $id
	 * @return Response
	 */
	public function show($id)
	{
		//
	}

}

Binding Interfaces To Implementations

A very powerful feature of the service container is its ability to bind an interface to a given implementation. For example, perhaps our application integrates with the Pusher web service for sending and receiving real-time events. If we are using Pusher's PHP SDK, we could inject an instance of the Pusher client into a class. First, let's register a binding for the SDK that binds it to an interface:

$app->bind('App\Contracts\EventPusher', 'App\Services\PusherEventPusher');

This tells the container that it should inject the PusherEventPusher when a class needs an implementation of EventPusher. Now we can type-hint the EventPusher interface in our constructor:

	/**
	 * Create a new order handler instance.
	 *
	 * @param  EventPusher  $pusher
	 * @return void
	 */
	public function __construct(EventPusher $pusher)
	{
		$this->pusher = $pusher;
	}

Contextual Binding

Sometimes you may have two classes that utilize the same interface, but you wish to inject different implementations into each class. For example, when our system receives a new Order, we may want to send an event via PubNub rather than Pusher. Lumen provides a simple, fluent interface for defining this behavior:

$app->when('App\Service\CreateOrder')
          ->needs('App\Contracts\EventPusher')
          ->give('App\Services\PubNubEventPusher');

Tagging

Occasionally, you may need to resolve all of a certain "category" of binding. For example, perhaps you are building a report aggregator that receives an array of many different Report interface implementations. After registering the Report implementations, you can assign them a tag using the tag method:

$app->bind('SpeedReport', function() {
	//
});

$app->bind('MemoryReport', function() {
	//
});

$app->tag(['SpeedReport', 'MemoryReport'], 'reports');

Once the services have been tagged, you may easily resolve them all via the tagged method:

$app->bind('ReportAggregator', function($app) {
	return new ReportAggregator($app->tagged('reports'));
});

Container Events

Registering A Resolving Listener

The container fires an event each time it resolves an object. You may listen to this event using the resolving method:

$app->resolving(function($object, $app) {
	// Called when container resolves object of any type...
});

$app->resolving(function(FooBar $fooBar, $app) {
	// Called when container resolves objects of type "FooBar"...
});

The object being resolved will be passed to the callback.