dirty generator

Author: sanmai

src/Helper/WindowIterator.php

@@ -50,7 +50,7 @@ class WindowIterator implements Iterator
 
     /**
      * @param Iterator<TKey, TValue> $inner
-     * @param int|null $maxSize Maximum buffer size (null = unlimited)
+     * @param int<1, max>|null $maxSize Maximum buffer size (null = unlimited)
      */
     public function __construct(
         private readonly Iterator $inner,
@@ -123,6 +123,13 @@ private function initialize(): void
         }
         $this->initialized = true;
 
+        // If inner is already pointing at data (e.g. a started generator), capture it
+        if ($this->inner->valid()) {
+            $this->pushFromInner();
+
+            return;
+        }
+
         $this->fetch(rewind: true);
     }
 
@@ -139,6 +146,11 @@ private function fetch(bool $rewind = false): void
             return;
         }
 
+        $this->pushFromInner();
+    }
+
+    private function pushFromInner(): void
+    {
         $this->buffer->push([$this->inner->key(), $this->inner->current()]);
     }
 }

src/Standard.php

@@ -691,7 +691,7 @@ public function cursor(): Iterator
      *
      * With a size limit, oldest elements are dropped (sliding window).
      *
-     * @param int|null $size Maximum buffer size (null = unlimited)
+     * @param int<1, max>|null $size Maximum buffer size (null = unlimited)
      * @return Iterator<TKey, TValue>
      */
     public function window(?int $size = null): Iterator

tests/WindowTest.php

@@ -408,4 +408,32 @@ public function valid(): bool
         $window->next();
         $this->assertSame(0, $nextCalls);
     }
+
+    public function testWindowWithStartedGenerator(): void
+    {
+        $generator = (function () {
+            yield 1;
+            yield 2;
+            yield 3;
+        })();
+
+        // Advance the generator - it's now "dirty"
+        $generator->next();
+        $this->assertSame(2, $generator->current());
+
+        // Wrapping in WindowIterator should not throw "Cannot rewind a generator"
+        $window = new WindowIterator($generator);
+
+        // Should capture current element (2) and continue
+        $collected = [];
+        foreach ($window as $value) {
+            $collected[] = $value;
+        }
+
+        $this->assertSame([2, 3], $collected);
+
+        // Can rewind and replay
+        $window->rewind();
+        $this->assertSame([2, 3], take($window)->toList());
+    }
 }