$component = 'user';
switch($component) {
    case PHP_URL_SCHEME:   case 'scheme':   $index = 'scheme';   break;
    case PHP_URL_HOST:     case 'host':     $index = 'host';     break;
    case PHP_URL_PORT:     case 'port':     $index = 'port';     break;
    case PHP_URL_USER:     case 'user':     $index = 'user';     break;
    case PHP_URL_PASS:     case 'pass':     $index = 'pass';     break;
    case PHP_URL_PATH:     case 'path':     $index = 'path';     break;
    case PHP_URL_QUERY:    case 'query':    $index = 'query';    break;
    case PHP_URL_FRAGMENT: case 'fragment': $index = 'fragment'; break;
}