Symfony 2：app_dev.php中@运算符的用途

Question

The default code that prevents access to debug front controller on production server is:

if (isset($_SERVER['HTTP_CLIENT_IP'])
    || isset($_SERVER['HTTP_X_FORWARDED_FOR'])
    || !(in_array(@$_SERVER['REMOTE_ADDR'], array('127.0.0.1', 'fe80::1', '::1')) || php_sapi_name() === 'cli-server')
) {
    header('HTTP/1.0 403 Forbidden');
    exit('You are not allowed to access this file. Check '.basename(__FILE__).' for more information.');
}

So the question is: Why would it be needed to supress warnings from @$_SERVER['REMOTE_ADDR']? The errors from other $_SERVER variables aren't supressed though.

Answer 1

First of all $_SERVER['REMOTE_ADDR'] could be empty (see this)

The errors are not suppressed from the others $_SERVER variables because are used inside the isset function. Using a variable (or accessing an element of an existing array) that is not set inside the isset function will not give an error or a warning since verifying if the variable is set is the role of the function itself.