implement true per-class singleton in AbstractSingleton, add hook to container build

Author: yuriipavlov

config/container.php

@@ -4,6 +4,8 @@
 
 $builder = new ContainerBuilder();
 
+$builder = apply_filters('starter_kit/container_builder', $builder);
+
 $builder->addDefinitions(require __DIR__ . '/dependencies.php');
 
 return $builder->build();

src/AbstractSingleton.php

@@ -7,17 +7,25 @@
  */
 abstract class AbstractSingleton
 {
+    /**
+     * Array of instances of singleton classes
+     *
+     * @var array
+     */
+    private static array $instances = [];
+
     /**
      * Call this method to get singleton
      */
-    public static function instance(): bool|static
+    public static function instance(): static
     {
-        static $instance = false;
-        if ($instance === false) {
-            $instance = new static();
+        $class = static::class;
+
+        if (!isset(self::$instances[$class])) {
+            self::$instances[$class] = new static();
         }
 
-        return $instance;
+        return self::$instances[$class];
     }
 
     /**

src/App.php

@@ -4,12 +4,12 @@
 
 defined('ABSPATH') || exit;
 
+use Psr\Container\ContainerInterface;
+use Psr\Log\LoggerInterface;
 use StarterKit\Base\Constants;
 use StarterKit\Base\Hooks;
-use StarterKit\Handlers\CLI\CLI;
 use StarterKit\Error\ErrorHandler;
-use Psr\Container\ContainerInterface;
-use Psr\Log\LoggerInterface;
+use StarterKit\Handlers\CLI\CLI;
 use Throwable;
 
 /**