introduced PostId and PostStatus and changed naming from Storage to Persistence

More/Repository/Domain/PostId.php

@@ -0,0 +1,42 @@
+<?php
+
+namespace DesignPatterns\More\Repository\Domain;
+
+/**
+ * This is a perfect example of a value object that is identifiable by it's value alone and
+ * is guaranteed to be valid each time an instance is created. Another important property of value objects
+ * is immutability.
+ *
+ * Notice also the use of a named constructor (fromInt) which adds a little context when creating an instance.
+ */
+class PostId
+{
+    /**
+     * @var int
+     */
+    private $id;
+
+    public static function fromInt(int $id)
+    {
+        self::ensureIsValid($id);
+
+        return new self($id);
+    }
+
+    private function __construct(int $id)
+    {
+        $this->id = $id;
+    }
+
+    public function toInt(): int
+    {
+        return $this->id;
+    }
+
+    private static function ensureIsValid(int $id)
+    {
+        if ($id <= 0) {
+            throw new \InvalidArgumentException('Invalid PostId given');
+        }
+    }
+}