docs: Notes about switching types in session (#9508)

* docs: Note about switching types in session

* docs: Apply suggestion

* docs:Grammar fix

Author: neznaika0

user_guide_src/source/libraries/sessions.rst

@@ -344,6 +344,13 @@ intend to reuse that same key in the same request, you'd want to use
 
 .. literalinclude:: sessions/036.php
 
+Changing the Session Key Type
+=============================
+
+Since session data values like Flashdata and Tempdata are differentiated only by internal flags, you can change a value's type without rewriting its data.
+
+.. literalinclude:: sessions/045.php
+
 Closing a Session
 =================
 

user_guide_src/source/libraries/sessions/045.php

@@ -0,0 +1,25 @@
+<?php
+
+session()->setFlashdata('alerts', 'Operation successful!');
+
+/*
+ * Get flash value 'Operation successful!' in another controller.
+ *
+ * echo session()->getFlashdata('alerts');
+ */
+
+// You can switch the session key type from Flashdata to Tempdata like this:
+session()->markAsTempdata('alerts');
+
+// Or simply rewrite it directly
+session()->setTempdata('alerts', 'Operation successful!');
+
+/*
+ * Get temp value 'Operation successful!' in another controller.
+ *
+ * echo session()->getTempdata('alerts');
+ *
+ * But flash value will be empty 'null'.
+ *
+ * echo session()->getFlashdata('alerts');
+ */