JpnForPhp\Transliterator\Romaji::transliterateChoonpu PHP Method

    protected function transliterateChoonpu($str, $parameters)
    {
        $keys = array_keys($parameters['macrons']);
        $pattern = '/([' . implode('', $keys) . '])ー/u';
        return preg_replace_callback($pattern, function ($matches) use($parameters) {
            return $parameters['macrons'][$matches[1]];
        }, $str);
    }