This would be more read friendly:

```php
if ($this->ssl && !function_exists('ftp_ssl_connect')) {
    throw new \RuntimeException('The function "ftp_ssl_connect" is not available');
}

$function = $this->ssl ? 'ftp_ssl_connect' : 'ftp_connect';
$this->connection = $function($this->host, $this->port);
```