Demystifying The Service Container

At the Laravel Mumbai meetup - May, 2019.

A deep understanding of the service container is essential to building a powerful, large application, as well as for contributing to the Laravel core itself. In my talk, I will share my knowledge that will help the audience with the former part resulting in them achieving the later part.

Transcript

1. Demystifying The Container Also known as the IOC container, DI container & Service container @introwit 1
2. "A deep understanding of the Laravel service container is essential to building a powerful, large application, as well as for contributing to the Laravel core itself." 1 Laravel documentation @introwit 2
3. Container @introwit 3
4. Storyline of this talk 4 Let's prepare some food ! 4 You enter the kitchen to see some spices are on the first shelf, some on second, etc " 4 Not enough funds to order from Uber Eats # Be the hero chef of your own story kitchen! @introwit 4
5. The Problem Spices are scattered. Have to reach out to different places again & again to get the spices. Put them back after the food is prepared. Repeat. It's not really in your control. The control is with the spices we are dependent on to prepare the food. @introwit 5
6. IOC Inversion Of Control You took all the spices and added them to a container with respective labels. Now you don't need to reach-out to or search at different places. You inverted the control. @introwit 6
7. DI Dependency Injection Now the need for all the things you are dependent upon can be fulfilled by that container. The container will inject the dependency in the food as per your needs. @introwit 7
8. "The Laravel service container is a powerful tool for managing class dependencies and performing dependency injection." 1 Laravel documentation @introwit 8
9. MasterChef or a Laravel meet-up? @introwit 9
10. app() @introwit 10
11. But why isn't it called container()? Because the instances app() method generates are of the class called Application, and that class extends the Container class. @introwit 11
12. So to create an instance of the container: $container = app(); @introwit 12
13. Resolving & Binding @introwit 13
14. Resolving things out of the container $car = app()->make(Car::class); vs $car = new Car; @introwit 14
15. Resolving things out of the container $car = app()->make(Car::class); vs $car = new Car(Engine $engine); @introwit 15
16. Resolving things out of the container $car = app()->make(Car::class); vs $car = new Car(Engine $engine(Oil $oil)); @introwit 16
17. The magic called "Reflection" ! @introwit 17
18. Reflection It's the ability of a programme to inspect & describe itself. Remember get_class($data) or get_class_methods(Car::class)? PS: There are many more PHP Reflection functions available. @introwit 18
19. How Laravel Uses Reflection? app()->make(Car::class); -> Get the list of dependencies. (The class Car has a dependency called $engine) -> Use the typehint and instantiate the dependency and pass it. (Use the Engine typehint to reach the class) @introwit 19
20. What if no typehints are available? :( We can manually bind things into the container. So that when a typehint is unavailable, our code doesn't break and fallbacks to check if we have defined some bindings for the same. @introwit 20
21. Assume $engine wasn't typehinted. class Car { function __construct($engine) {} } app()->make(Car::class) would then fail since it wouldn't know what exactly $engine is? @introwit 21
22. Binding things into the container app()->bind(Car::class, function () { return new Car(new Engine); }); Now when we do app()->make(Car::class) or whenever Car::class is resolved out of the container, it would run the callback above and return what we define. @introwit 22
23. What else? @introwit 23
24. Contextual Binding $this->app->when(PhotoController::class) ->needs(Filesystem::class) ->give(function () { return Storage::disk('local'); }); $this->app->when([VideoController::class, UploadController::class]) ->needs(Filesystem::class) ->give(function () { return Storage::disk('s3'); }); @introwit 24
25. Container Events $this->app->resolving(function ($object, $app) { // Called when container resolves object of any type... }); $this->app->resolving(Storage::class, function ($api, $app) { // Called when container resolves object of "Storage" class... // Useful for things like setting up some props or credentials/authentication with the object }); @introwit 25
26. Few more container goodies 4 You can bind anything into the container, something as simple as a dynamic key-value pair: app()->bind('random-string', function ($app, $params) { return str_random($params['length']); }); // app()->makeWith('random-string', ['length' => 5]); 4 Easily Swap Implementations. @introwit 26
27. @introwit @introwit 27