When and Why Does PHP Use Function Reference Parameters?

Understanding Function Reference Parameter in PHP

In PHP, you can prefix a function name with an ampersand (&). This signifies that the function will return a reference to a variable rather than the value itself. While it may seem counterintuitive, there are scenarios where returning by reference is advantageous.

Let's examine an example from the Facebook REST Client library:

public function &users_hasAppPermission($ext_perm, $uid=null) {
    return $this->call_method('facebook.users.hasAppPermission',
        array('ext_perm' => $ext_perm, 'uid' => $uid));
}

Here, the function users_hasAppPermission returns a reference to a variable. However, to understand how to use this library effectively, let's construct a simple example:

$facebook = new FacebookRestClient();
$result = &$facebook->users_hasAppPermission('email');

if ($result) {
    // The 'email' extended permission is granted
} else {
    // The 'email' extended permission is not granted
}

In this snippet, we create a reference to the variable returned by the users_hasAppPermission function. The $result variable now contains a reference to the same variable that stores the permission status. This allows us to manipulate the permission status directly through the $result variable.

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