PHP has many different error levels, a few of which get ignored by a lot of developers I know. In particular, some of the developers I know don’t really care about E_STRICT. When developing their applications, they tend to take care of the errors that halt execution (E_ERROR) but don’t care that much about “the little things” like an unmatched method signature or calling a non-static method statically. What’s the big deal, right? The PHP documentation further propogates this idea that E_STRICT isn’t that important by saying that E_STRICT errors are:

suggest[ed] changes to your code which will ensure the best interoperability and forward compatibility

If it’s just a suggestion, who’s to say PHP is right? I mean I know my code and its purposes better than the PHP parser - why should I take the advice?

Well there’s actually good reasons to take care of all E_STRICT errors that you see on your site. (You should even take care of the ones you don’t see, hidden ones that only get logged to your error_log file.) The major benefit that I’ll focus on today is “forward compatibility”.

Forward Compatibility

Fixing any E_STRICT errors helps make your code forward compatible. We’ve all heard that large projects should worry about keeping their code “backward compatible” so that others who use it and depend on it don’t have a hard time keeping up with the breaking changes, but what is this about forward compatibility?

In its simplest form, forward compatible code is ready to do its best to take on the future, whatever may happen. It’s being proactive about your code and staying on top of changes in upcoming releases. It’s making sure you’re following best practices and suggestions in order to protect yourself from potential backward compatibility issues. It’s taking the information you have available and writing your best code with it in order to be prepared.

That definitely sounds like “a good thing^tm”, right? While many developers want to achieve those things, they don’t do the things necessary in order to accomplish them. One of the things you can do to better ensure forward compatibility is to take care of E_STRICT errors on your site, rather than brushing them off as useless suggestions.

For example, you’ve probably seen the following error before on your site:

Error: Declaration of YourCustomClass::store() should be compatible with that of ConcreteClassYouAreExtending::store($updateNulls = false)

What this means is that when you were writing your code, you didn’t match the method signature ¹ in your custom class with that of the parent class. The reason this is a problem is that your custom class becomes very narrowly focused and is not able to be reused in other places where a class that extended the parent class would be able to be used.

Furthermore, it prevents progress in the code at the architecture level. As we’ve already learned, when you extend a base class and don’t match the signature, it’s “just an E_STRICT” error; application execution doesn’t stop. However, if you wanted to start improving application architecture by starting to [program to an interface] [3], not following method signature can now throw a fatal error. Consider the following code.

<?php

class BaseController
{
    public function getAction($id = null)
    {
        // do stuff with the $id
    }
}

class UserController extends BaseController
{
    public function getAction()
    {
        // get the id from a request object instead
        $id = $this->input->get('id');
        
        // do stuff with $id
    }
}

With that code, if you had E_STRICT enabled for reporting, you’d see the “X doesn’t match method signature of Y” error that I noted earlier. No big deal, it still runs, right? Well let’s assume that the BaseController presented above is part of a framework, and the UserController is your custom code. So now the framework wants to start programming to an interface, so it creates ControllerInterface and implements that in the BaseController.

<?php

interface ControllerInterface
{
    public function getAction($id = null);
}

class BaseController implements ControllerInterface
{
    public function getAction($id = null)
    {
        // do stuff with $id
    }
}

When the framework developer runs the unit tests, everything is just fine, because the method signatures match that of the interface and no errors are thrown. An update is released and you go ahead and apply it, since it was just a new patch release anyways, nothing should break, only to find that the E_STRICT error you had been ignoring is now an E_ERROR that breaks your application. Oh yeah, did I forgot to mention that you applied this update in production on a Friday afternoon at 4:45 PM, which you now have to fix before you can leave for the weekend?

All of that could have been avoided if you just fixed the E_STRICT error, but you instead chose to ignore it. Forward compatibility is worth a 2 min code change, don’t you think?

declaration. Think of it as the fingerprint of the method. It’s always the same, and extending classes should keep it the same as well. [3]: http://www.php5dp.com/design-pattern-principles-for-php-program-to-an-interface-not-an-implementation/ “Program to an Interface, not an implementation”