Pinq\Iterators\IIteratorScheme::projectionIterator PHP Метод

    public function projectionIterator(\Traversable $iterator, callable $keyProjectionFunction = null, callable $valueProjectionFunction = null);

 private function mapIterator(callable $function = null)
 {
     if ($function === null) {
         return $this->elements;
     } else {
         return $this->scheme->projectionIterator($this->elements, null, $function);
     }
 }