PHP Solution for “Can’t use method return value in write context”

I was getting this error while trying to do this in php:

if empty($userSession = $this->Session->read('User')) { //do something; }

The solution to get over this is to define a variable before actually testing for its value, as such.

$userSession = $this->Session->read('User');
if empty($userSession) { // do something; }

As a rule of thumb, the php function empty cannot check the return value of a function or method. It can only check variables.