Understanding IoC, Simple Factory, and Dependency Injection in PHP

The article introduces the IoC (Inversion of Control) pattern as a way to solve component dependencies, using a school‑going scenario where a Student needs a Go_To_School implementation.

First, a simple interface interface Go_To_School { public function go(); } is defined, followed by concrete classes Foot, Car, and Bicycle that implement this interface, each printing a different message.

A Student class is then shown with a private $trafficTool property. The constructor manually creates a Foot instance, illustrating tight coupling and the need for a better solution.

To reduce coupling, a simple factory

class TrafficToolFactory { public function createTrafficTool($name) { switch($name) { case 'Foot': return new Foot(); case 'Car': return new Car(); case 'Bicycle': return new Bicycle(); default: exit('set trafficTool error!'); } } }

is introduced, and the Student constructor receives a traffic‑tool instance via dependency injection.

Finally, a minimal IoC container is presented. The container stores bindings with $ioc->bind('Go_To_School', 'Car'); and $ioc->bind('student', 'Student');, and resolves them using $student = $ioc->make('student'); $student->go_to_school();. The container can also bind callbacks, e.g.,

$ioc->bind('Go_To_School', function() { return new Car(); });

, allowing flexible creation of dependencies.

Through these examples, the article demonstrates how moving object creation out of classes and into factories or an IoC container eliminates hard‑coded dependencies, making the codebase easier to maintain and extend.