Made LinkedList traversable via Iterator interface

Author: Alienpruts

chap-03/linked-lists.php

@@ -72,3 +72,10 @@
 // Retrieve the 2nd item from the list
 echo $bookTitles->getItemByPosition(2)->data;
 echo SEPERATOR;
+
+// We've made the list Iterable, reverse list again and loop through it.
+$bookTitles->reverse();
+foreach ($bookTitles as $title){
+    echo $title . PHP_EOL;
+}
+

src/Chapter03/LinkedList.php

@@ -9,10 +9,12 @@
 namespace App\Chapter03;
 
 
-class LinkedList
+class LinkedList implements \Iterator
 {
     private $_firstNode = NULL;
     private $_totalNodes = 0;
+    private $_currentNode = NULL;
+    private $_currentPosition = 0;
 
     public function insert(string $data = NULL)
     {
@@ -268,4 +270,61 @@ public function getItemByPosition(int $position = 0)
 
     }
 
+    /**
+     * Return the current element
+     * @link https://php.net/manual/en/iterator.current.php
+     * @return mixed Can return any type.
+     * @since 5.0.0
+     */
+    public function current()
+    {
+        return $this->_currentNode->data;
+    }
+
+    /**
+     * Move forward to next element
+     * @link https://php.net/manual/en/iterator.next.php
+     * @return void Any returned value is ignored.
+     * @since 5.0.0
+     */
+    public function next()
+    {
+        $this->_currentPosition++;
+        $this->_currentNode = $this->_currentNode->next;
+    }
+
+    /**
+     * Return the key of the current element
+     * @link https://php.net/manual/en/iterator.key.php
+     * @return mixed scalar on success, or null on failure.
+     * @since 5.0.0
+     */
+    public function key()
+    {
+        return $this->_currentPosition;
+    }
+
+    /**
+     * Checks if current position is valid
+     * @link https://php.net/manual/en/iterator.valid.php
+     * @return boolean The return value will be casted to boolean and then evaluated.
+     * Returns true on success or false on failure.
+     * @since 5.0.0
+     */
+    public function valid()
+    {
+        return $this->_currentNode !== NULL;
+    }
+
+    /**
+     * Rewind the Iterator to the first element
+     * @link https://php.net/manual/en/iterator.rewind.php
+     * @return void Any returned value is ignored.
+     * @since 5.0.0
+     */
+    public function rewind()
+    {
+        $this->_currentPosition = 0;
+        $this->_currentNode = $this->_firstNode;
+    }
 }