How do you stop a PHP class from executing?

Question

I'm looking for something like break for loops.

Here's some example code (using Symfony's lime) where stop() would not let the class continue and I_DONT_WANT_THIS_TO_RUN() would not be executed.

$browser->isStatusCode(200)
  ->isRequestParameter('module', 'home')
  ->isRequestParameter('action', 'index')
  ->click('Register')
  ->stop()
  ->I_DONT_WANT_THIS_TO_RUN();
$browser->thenThisRunsOkay();

Calling $this->__deconstruct(); from within stop() doesn't seem to do the trick. Is there a function I can call within stop() that would make that happen?

Answer 1

You could use PHP exceptions:

// This function would of course be declared in the class
function stop() {
    throw new Exception('Stopped.');
}

try {
    $browser->isStatusCode(200)
      ->isRequestParameter('module', 'home')
      ->isRequestParameter('action', 'index')
      ->click('Register')
      ->stop()
      ->I_DONT_WANT_THIS_TO_RUN();
} catch (Exception $e) {
    // when stop() throws the exception, control will go on from here.
}

$browser->thenThisRunsOkay();

Answer 2

Just return another class which will return $this for every method called.

Example:

class NoMethods {
    public function __call($name, $args)
    {
        echo __METHOD__ . " called $name with " . count($args) . " arguments.\n";
        return $this;
    }
}

class Browser {
    public function runThis()
    {
        echo __METHOD__ . "\n";
        return $this;
    }

    public function stop()
    {
        echo __METHOD__ . "\n";
        return new NoMethods();
    }

    public function dontRunThis()
    {
        echo __METHOD__ . "\n";
        return $this;
    }
}

$browser = new Browser();
echo "with stop\n";
$browser->runThis()->stop()->dontRunThis()->dunno('hey');
echo "without stop\n";
$browser->runThis()->dontRunThis();
echo "the end\n";

Will result in:

with stop
Browser::runThis
Browser::stop
NoMethods::__call called dontRunThis with 0 arguments.
NoMethods::__call called dunno with 1 arguments.
without stop
Browser::runThis
Browser::dontRunThis
the end

Answer 3

OIS's answer is really good, though I could see that it might get confusing if the object suddenly changes to something else. That is, you'd expect that at the end of your chain, you'll end up with the same object. To avoid that problem, I'd add a private variable to tell the class whether or not to actually do anything. If the class has been stopped, then every class just returns $this straight away. This gives you the added benefit of being able to restart the execution.

class MyClass {
    private $halt;

    function __call($func, $args) {
        if ($this->halt) {
            return $this;
        } else {
            return $this->$func($args);
        }
    }

    private function isRequestParameter() {
        // ...
    }
    public function stop() {
        $this->halt = true;
    }
    public function start() {
        $this->halt = false;
    }
}

This could be put into a parent class so you don't have to duplicate this code.