code: public function each(callable $callable)
      {
          foreach ($this->items as $key => $item) {
              if ($callable($item, $key) === false) {
                  break;
              }
              $this->items[$key] = $item;
          }
          return $this;
      }
docs: Run a callable/closure on each element.
  
  @param callable $callable Parameters: ($item, $key). Prefix $item with & to modify $item.
  @return $this
  @throws \Exception