Code Quality Metrics

Wouldn’t it be great if we could measure the quality of our software? Software developers often want to improve their software again and again – but maybe it is already “good enough.” How do we know when it reaches a good state?

Software quality metrics were introduced by smart people in the early days of programming. In the 1970s, they thought about this topic and produced the ideas that are still in use today. Of course, we want to benefit from this knowledge and apply it to our own projects.

In this chapter, we are going to cover the following topics:

• Introducing code quality metrics
• Gathering metrics in PHP
• The pros and cons of using metrics

Technical requirements

If you have gone through the previous chapter and tried out all the tools, you already have everything that you need for this chapter installed. If not, please make sure to do so before you run the upcoming examples.

The code files for this chapter can be found here: https://github.com/PacktPublishing/Clean-Code-in-PHP

Introducing code quality metrics

In this section, you will learn about how to measure the quality of software in general. We will look at some of the most used metrics in the PHP world and explain what they can tell you about your code, how to gather them, and when they are useful or not.

Aspects of software quality

Before we dive into the numbers, we need to clarify one important thing first: what does software quality actually mean? Surely, everybody has a certain understanding of quality, but it might be hard to put this in words. Luckily, there are already existing models, such as the FURPS model, which was developed at Hewlett-Packard back in the 1980s. The acronym stands for the following:

• Functionality: Is the software capable of dealing with a wide variety of use cases? Has it been developed with security in mind?
• Usability: How good is the user experience? Is it documented and easy to understand?
• Reliability: Is the software available at all times?...

Gathering metrics in PHP

In this section, we want to have a look at the tools there are in the PHP world to gather code quality metrics. As you will see shortly, these metrics are not just numbers – they will allow you to make educated guesses about how much effort it will take to refactor code. They will also help you to identify the parts of the code that will require the most attention.

Again, we have curated a selection of tools for you:

• phploc
• PHP Depend
• PhpMetrics

phploc

As we learned in the previous section, the abbreviation LOC stands for lines of code, so the name already reveals the main purpose of this tool. Being a basic metric, it already tells us quite a few things about a code base. phploc also provides further metrics, such as the CC, so it is worth having a closer look at it.

Installation and usage

The author of this tool, Sebastian Bergmann, is well known for phpunit, the de facto standard for automated tests in the PHP world...

The pros and cons of using metrics

In the two previous chapters of this book, you have learned about many tools and metrics that exist solely to help you write better software. The knowledge and wisdom and countless hours of endeavor on the part of hundreds if not thousands of software engineers can be added to your project in a matter of minutes.

The other side of the coin is that you might already feel completely overwhelmed by the sheer number of possibilities. Which tools should you choose? Which metrics should you focus on in the future?

If you have that feeling already, do not worry. We will not leave you alone in all this mess but help you find a setup that fits your needs during the next chapters. To begin with, let us take the time to look at the pros but also cons of using code quality metrics.

The pros

First, each software project is a unique piece of work. It grows based on certain circumstances, such as the skill sets of the developers and the available packages...

Summary

This chapter introduced you to some of the most used code quality metrics in the PHP world. Furthermore, we presented you with the tools that help you gather them. Of course, there are many more that we could not cover in this book, but you do not have to know them all – you are now equipped with a solid understanding of code quality metrics that will help you in your daily working routine.

Code quality tools and metrics are surely no silver bullet for all problems. On the one hand, they can be extremely helpful for improving your code. On the other hand, you should not take them as the ultimate measure. There are numerous examples of successful types of software that would never pass these quality checks, such as WordPress. Be sure, though, that the creators of WordPress would have done things differently if they had known beforehand.

In the next chapter, we will leave the realm of theory. We will learn how to organize the tools that we introduced in the last...

Further reading

• dePHPend (https://dephpend.com/) is a tool that can draw UML diagrams for your PHP code and be used to spot problems in your architecture.