Refactor singleton functionality into trait

server/libs/FileDownloader.php

@@ -1,19 +1,6 @@
 <?php
 
 class FileDownloader extends FileManager {
-
-    private static $instance = null;
-
-    public static function getInstance() {
-        if (self::$instance === null) {
-            self::$instance = new FileDownloader();
-        }
-
-        return self::$instance;
-    }
-
-    private function __construct() {}
-
     public function download() {
         $fullFilePath = $this->getFullFilePath();
 

server/libs/FileManager.php

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

server/libs/FileUploader.php

@@ -8,16 +8,6 @@ class FileUploader extends FileManager {
     private $permission;
     private $storage;
 
-    private static $instance = null;
-
-    public static function getInstance() {
-        if (self::$instance === null) {
-            self::$instance = new FileUploader();
-        }
-
-        return self::$instance;
-    }
-
     private function __construct() {
         $this->storage = new \Upload\Storage\FileSystem($this->getLocalPath());
     }

server/libs/MailSender.php

@@ -1,17 +1,9 @@
 <?php
 class MailSender {
+    use SingletonTrait;
 
     private $mailOptions = [];
     private $mailerInstance;
-    private static $instance = NULL;
-
-    public static function getInstance() {
-        if(MailSender::$instance === NULL) {
-            MailSender::$instance = new MailSender();
-        }
-
-        return MailSender::$instance;
-    }
 
     private function __construct() {
         $this->setConnectionSettings(

server/libs/SingletonTrait.php

@@ -0,0 +1,18 @@
+<?php
+
+trait SingletonTrait
+{
+    private static $instance;
+
+    private function __construct()
+    {
+    }
+
+    public static function getInstance()
+    {
+        if (!isset(static::$instance)) {
+            static::$instance = new static();
+        }
+        return static::$instance;
+    }
+}

server/models/Session.php

@@ -1,7 +1,8 @@
 <?php
 
 class Session {
-    static $instance = null;
+    use SingletonTrait;
+
     private $sessionPrefix = '';
     
     private function __construct() {
@@ -17,14 +18,6 @@ class Session {
         session_destroy();
     }
 
-    public static function getInstance() {
-        if (!self::$instance) {
-            self::$instance = new Session();
-        }
-
-        return self::$instance;
-    }
-
     public function createSession($userId, $staff = false) {
         $this->store('userId', $userId);
         $this->store('staff', $staff);