Improved singleton implementation

server/libs/FileDownloader.php

@@ -1,6 +1,8 @@
 <?php
 
 class FileDownloader extends FileManager {
+    use SingletonTrait;
+
     public function download() {
         $fullFilePath = $this->getFullFilePath();
 

server/libs/FileManager.php

@@ -1,7 +1,6 @@
 <?php
 
 abstract class FileManager {
-    use SingletonTrait;
     private $fileName;
     private $localPath = 'files/';
 

server/libs/FileUploader.php

@@ -1,13 +1,14 @@
 <?php
 
 class FileUploader extends FileManager {
+    use SingletonTrait;
+
     private $maxSize = 1;
     private $fileName;
     private $permission;
     private $storage;
 
-    protected function __construct() {
-        parent::__construct();
+    private function __construct() {
         $this->storage = new \Upload\Storage\FileSystem($this->getLocalPath());
     }
 

server/libs/SingletonTrait.php

@@ -1,10 +1,15 @@
 <?php
 
+/**
+ * Trait SingletonTrait
+ * This trait helps implementing singleton classes
+ * It must be used on each class in a hierarchy that needs to be a singleton
+ */
 trait SingletonTrait
 {
-    private static $instance;
+    protected static $instance;
 
-    protected function __construct()
+    private function __construct()
     {
     }