Update Cycle operation.

spec/loophp/collection/CollectionSpec.php

@@ -409,20 +409,21 @@ public function it_can_count_its_items(): void
 
     public function it_can_cycle(): void
     {
-        $this
-            ->beConstructedThrough('with', [['1', '2', '3']]);
-
-        $this
+        $this::with(['1', '2', '3'])
             ->cycle(3)
             ->shouldIterateAs(['1', '2', '3']);
 
-        $this
+        $this::with(['1', '2', '3'])
             ->cycle(6)
             ->shouldIterateAs(['1', '2', '3', '1', '2', '3']);
 
-        $this
+        $this::with(['1', '2', '3'])
             ->cycle(7)
             ->shouldIterateAs(['1', '2', '3', '1', '2', '3', '1']);
+
+        $this::with(['1', '2', '3'])
+            ->cycle()
+            ->shouldIterateAs([]);
     }
 
     public function it_can_distinct(): void

src/Collection.php

@@ -140,7 +140,7 @@ public function count(): int
         return $this->transform(new Count());
     }
 
-    public function cycle(int $length = 0): BaseInterface
+    public function cycle(?int $length = null): BaseInterface
     {
         return $this->run(new Cycle($length));
     }

src/Contract/Operation/Cycleable.php

@@ -8,8 +8,5 @@
 
 interface Cycleable
 {
-    /**
-     * @return \loophp\collection\Base|\loophp\collection\Contract\Collection
-     */
-    public function cycle(int $length = 0): Base;
+    public function cycle(?int $length = null): Base;
 }

src/Operation/Cycle.php

@@ -13,14 +13,18 @@
 
 final class Cycle extends AbstractOperation implements Operation
 {
-    public function __construct(int $length = 0)
+    public function __construct(?int $length = null)
     {
-        $this->storage['length'] = $length;
+        $this->storage['length'] = $length ?? 0;
     }
 
     public function __invoke(): Closure
     {
         return static function (iterable $collection, int $length): Generator {
+            if (0 === $length) {
+                return yield from [];
+            }
+
             $iterator = new LimitIterator(
                 new InfiniteIterator(
                     new IterableIterator($collection)
@@ -29,8 +33,8 @@ public function __invoke(): Closure
                 $length
             );
 
-            foreach ($iterator as $value) {
-                yield $value;
+            foreach ($iterator as $key => $value) {
+                yield $key => $value;
             }
         };
     }