Sample of implementing an IoC container for dependency injection

composer.json

@@ -2,7 +2,9 @@
     "name": "grikdotnet/monolith-decomposition",
     "type": "project",
     "require": {
-        "php": "^7.4"
+        "php": "^8.0",
+        "symfony/dependency-injection": "^5.2",
+        "symfony/config": "^5.2"
     },
     "autoload": {
         "psr-4": {

public/index.php

@@ -1,7 +1,27 @@
 <?php
 
+use Symfony\Component\Config\FileLocator;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Loader\PhpFileLoader;
+
 include '../vendor/autoload.php';
 
-// Usually an application kernel and is called here,
-// it calls routing, then some middleware, and then controllers
-new Acme\ImageResizeController();
+// Usually an application kernel creates
+// an IoC-container, routing, some middleware, and controllers,
+// but I'll just create a container and a controller drectly.
+
+$containerBuilder = new ContainerBuilder();
+$loader = new PhpFileLoader($containerBuilder, new FileLocator('..'));
+$loader->load('services.php');
+$containerBuilder->compile();
+// in a real project there will be some cacheing of the container
+// file_put_contents($file, (new PhpDumper($containerBuilder))->dump());
+
+try {
+    $controller = $containerBuilder->get(\Acme\ImageResizeController::class);
+} catch (Exception $e) {
+    echo $e->getMessage(),"\n",$e->getTraceAsString();
+    exit;
+}
+
+$controller->action($_GET['id']?:null);

services.php

@@ -0,0 +1,14 @@
+<?php
+
+namespace Symfony\Component\DependencyInjection\Loader\Configurator;
+
+return function(ContainerConfigurator $configurator) {
+    /**
+     * @see https://symfony.com/doc/current/service_container/autowiring.html
+     */
+    $services = $configurator->services()->defaults()->autowire()->public();
+
+    $services->load('Acme\\', './src/*')
+        ->exclude('./src/BaseModel.php');
+
+};

src/Image.php

@@ -8,7 +8,8 @@
  */
 class Image extends \BaseModel
 {
-    public function __construct($filename)
+
+    public function load(mixed $tmp_name)
     {
         // calls to inherited methods
         $this->foo();

src/ImageResizeController.php

@@ -6,9 +6,13 @@
 
 class ImageResizeController
 {
-    public function __construct()
+    public function __construct(
+        public Image $image
+    ){
+    }
+
+    public function action(?string $id)
     {
-        $Image = new Image($_GET['id']?:null);
-        // other code skipped ...
+        $this->image->load($id);
     }
 }