Implement iterator interface for node collection

src/NodeFilter/NodeCollection.php

@@ -13,6 +13,7 @@ final class NodeCollection implements NodeFilter
     use Traits\EnumeratesValues;
 
     private DOMNodeList $nodes;
+    private int $iteratorPosition = 0;
 
     /**
      * @throws Exception When node could not be imported into a new document.
@@ -200,4 +201,29 @@ public function xPath(string $selector): NodeFilter
     {
         return $this->internalXpath($this->nodes, $selector);
     }
+
+    public function current(): NodeFilter
+    {
+        return $this->nth($this->iteratorPosition);
+    }
+
+    public function next(): void
+    {
+        $this->iteratorPosition++;
+    }
+
+    public function key(): int
+    {
+        return $this->iteratorPosition;
+    }
+
+    public function valid(): bool
+    {
+        return $this->current()->exists();
+    }
+
+    public function rewind(): void
+    {
+        $this->iteratorPosition = 0;
+    }
 }

src/NodeFilter/NodeFilter.php

@@ -4,7 +4,8 @@
 
 use Closure;
 
-interface NodeFilter
+/** @extends \Iterator<int, NodeFilter> */
+interface NodeFilter extends \Iterator
 {
     /**
      * Get the value for the requested attribute of the first node in the current collection.

src/NodeFilter/NullNode.php

@@ -97,4 +97,27 @@ public function xPath(string $selector): NodeFilter
     {
         return $this;
     }
+
+    public function current(): NodeFilter
+    {
+        return $this;
+    }
+
+    public function next(): void
+    {
+    }
+
+    public function key(): int
+    {
+        return 0;
+    }
+
+    public function valid(): bool
+    {
+        return false;
+    }
+
+    public function rewind(): void
+    {
+    }
 }

tests/NodeFilter/NodeCollectionTest.php

@@ -236,4 +236,15 @@ private function createDOMNodes(): DOMNodeList
 
         return $doc->childNodes;
     }
+
+    /** @test */
+    public function it_should_iterate_zero_times(): void
+    {
+        $text = '';
+        foreach ($this->node->querySelector('li') as $t) {
+            $text .= $t->text();
+        }
+
+        $this->assertEquals('onetwothreefour', $text);
+    }
 }

tests/NodeFilter/NullNodeTest.php

@@ -15,6 +15,17 @@ protected function setUp(): void
         $this->node = new NullNode();
     }
 
+    /** @test */
+    public function it_should_iterate_zero_times(): void
+    {
+        $count = 0;
+        foreach ($this->node as $n) {
+            $count += $n->count() + 1;
+        }
+
+        $this->assertEquals(0, $count);
+    }
+
     /** @test */
     public function it_should_return_empty_array_on_each(): void
     {