src/Zicht/Itertools/lib/Traits/KeysTrait.php
public function keys()
    {
        $keys = [];
        if ($this instanceof \Traversable) {
            foreach ($this as $key => $value) {
                $keys [] = $key;
            }
        }
        return $keys;
    }
public function keys()
    {
        $keys = [];
        if ($this instanceof \Traversable) {
            foreach ($this as $key => $value) {
                $keys [] = $key;
            }
        }
        return $keys;
    }
Returns an array with keys from this iterator

@return array