Pinq\Iterators\Standard\JoinIterator::doFetch PHP Метод

    protected function doFetch()
    {
        while ((list($innerKey, $innerValue) = $this->innerValuesIterator->fetch()) === null) {
            if ((list($this->outerKey, $this->outerValue) = $this->outerIterator->fetch()) === null) {
                return null;
            }
            $this->innerValuesIterator = $this->getInnerValuesIterator($this->outerKey, $this->outerValue);
            $this->innerValuesIterator->rewind();
        }
        $projectionFunction = $this->projectionFunction;
        return [$this->count++, $projectionFunction($this->outerValue, $innerValue, $this->outerKey, $innerKey)];
    }