Question

Let’s say we have a method signature like

public static function explodeDn($dn, array &$keys = null, array &$vals = null,     $caseFold = self::ATTR_CASEFOLD_NONE) 

we can easily call the method by omitting all parameters after $dn:

$dn=Zend_Ldap_Dn::explodeDn('CN=Alice Baker,CN=Users,DC=example,DC=com'); 

We can also call the method with 3 parameters:

$dn=Zend_Ldap_Dn::explodeDn('CN=Alice Baker,CN=Users,DC=example,DC=com', $k, $v); 

and with 4 parameters:

$dn=Zend_Ldap_Dn::explodeDn('CN=Alice Baker,CN=Users,DC=example,DC=com', $k, $v,      Zend_Ldap_Dn::ATTR_CASEFOLD_UPPER); 

But why is it impossible to call the method with the following parameter combination for example:

$dn=Zend_Ldap_Dn::explodeDn('CN=Alice Baker,CN=Users,DC=example,DC=com', $k, null,      Zend_Ldap_Dn::ATTR_CASEFOLD_UPPER); $dn=Zend_Ldap_Dn::explodeDn('CN=Alice Baker,CN=Users,DC=example,DC=com', null, $v); 

What’s the difference between passing null to the method and relying on the default value? Is this constraint written in the manual? Can it be circumvented?

Answer 1

It’s because you can’t have a reference to null.

You can have a reference to a variable that contains null – that is exactly what the default value does. Or you can pass in null as a literal value – but since you want an out parameter this is not possible here.