Five Reasons Object-Oriented Design Makes Sense for PHP

Editor’s Note: Today we have a guest post from Brandon Savage, an expert in crafting maintainable PHP applications. We invited Brandon to post on the blog to share some of his wisdom around bringing object-oriented design to PHP, a language with procedural roots.

One of the most common questions that PHP developers have about object-oriented programming is, “why should I bother?” Unlike languages such as Python and Ruby, where every string and array is an object, PHP is very similar to its C roots, and procedural programming is possible, if not encouraged.

Even though an object model exists in PHP, it’s not a requirement that developers use it. In fact, it’s possible to build great applications (see WordPress) without object-orientation at all.

So why bother?

There are five good reasons why object-oriented PHP applications make sense, and why you should care about writing your applications in an object-oriented style.

1. Objects are extensible.

It should be possible to extend the behavior of objects through both composition and inheritance, allowing objects to take on new life and usefulness in new settings.

Of course, developers have to be careful when extending existing objects, since changing the public API of an object creates a whole new object type. But, if done well, developers can revitalize old libraries through the power of inheritance.

2. Objects are replaceable.

The whole point of object-oriented development is to make it easy to swap objects out for one another. The Liskov Substitution Principle tells us that one object should be replaceable with another object of the same type and that the program should still work.

It can be hard to see the value in removing a component and replacing it with another component, especially early on in the development lifecycle. But the truth is that things change; needs, technologies, resources. There may come a point where you’ll need to incorporate a new technology, and having a well-designed object-oriented application will only make that easier.

3. Objects are testable.

It’s possible to test procedural applications, albeit not well. Most procedural applications don’t have an easy way to separate external components (like the file system, database, etc.) from the components under test. This means that under the best circumstances, testing a procedural application is more of an integration test than a unit test.

Object-oriented development makes unit testing far easier and more practical. Since you can easily mock and stub objects (see Mockery, a great mock object library), you can replace the objects you don’t need and test the ones you do. Since a unit test should be testing only one segment of code at a time, mock and stub objects make this possible.

4. Objects are maintainable.

There are a few problems with procedural code that make it more difficult to maintain. One is the likelihood of code duplication, that insidious parasite of unmaintainability. Object-oriented code, on the other hand, makes it easy for developers to put code in one place, and to create an expressive API that explains what the code is doing, even without having to know the underlying behavior.

Another problem that object-oriented programming solves is the fact that procedural code is often complicated. Multiple conditional statements and varying paths create code that is hard to follow. There’s a measure of complexity — cyclomatic complexity — that shows us the number of decision points in the code. A score greater than 12 is usually considered bad, but good object-oriented code will generally have a score under 6.

For example, if you know that a method accepts an object as one of its arguments, you don’t have to know anything about how that object works to meet the requirements. You don’t have to format that object, or manipulate the data to meet the needs of the method; instead, you can just pass the object along. You can further manipulate that object with confidence, knowing that the object will properly validate your inputs as valid or invalid, without you having to worry about it.

5. Objects produce catchable (and recoverable) errors.

Most procedural PHP developers are passingly familiar with throwing and catching exceptions. However, exceptions are intended to be used in object-oriented development, and they are best used as ways to recover from various error states.

Exceptions are catchable, meaning that they can be handled by our code. Unlike other mechanisms in PHP (like trigger_error()), we can decide how to handle an exception and determine if we can move forward (or terminate the application).

The Bottom Line

Object-oriented programming opens up a whole world of new possibilities for developers. From testing to extensibility, writing object-oriented PHP is superior to procedural development in almost every respect.