在PHP中杀死方法链

hi i have a method chain in php somewhat like

<?php
auth::('username') -> is_logged() -> doSomething();
//execute something
?>

what i would like to do is if the user is not logged then not invoke the doSomething() function. One way is to unset $this but that would generate an error id there any other way to do it. Also i cant be using die() because it would stop the compiler and prevent codes written afterwards from executing. What is the best way to do it preferably without any warning or error and at the same time making as few changes as possible because of a large number of functions associated with the class.

Return NullObject which will provide empty implementation of doSomething

In PHP you only need to provide the magic __call() method, so any function call will pass.

class NullObject {
    public function __call($name, $arguments) {
        return $this;
    }
}

To use it in your class:

public function is_logged() {
    if ($this->user_is_logged()) {
        return $this;
    } else {
        return new NullObject;
    }
}