Can't use the method return value in write context

Question

I'm using codeigniter and trying to make an if statement for if the controllers have changed. What I have right now gives the error.

if (isset($this->session->userdata('lastUrl')) && $this->session->userdata('lastUrl') != $this->router->class) {
     echo 'new controller';
}

$this->session->set_userdata('lastUrl', $this->router->class);

This code is in the constructor of the controller so it will be run on every page.

Answer 1

isset is a special language construct that can only be used on variables or array keys, not methods. This should have the same functionality:

$this->session->userdata('lastUrl') !== null && ...

Answer 2

you can check this by method_exists() function

if (method_exists($this->session->userdata('lastUrl')) && $this->session->userdata('lastUrl') != $this->router->class) {
     echo 'new controller';
}