Summary

In this chapter, you learned how you can use functions that are built into PHP to accomplish many tasks that would otherwise require you to write a lot of code to do the same thing much less quickly. You also learned various ways to write your own functions: with and without parameters, using default values or not, or even with varying amounts of parameters. You gained an understanding of functions that are pure and do not meddle with global scope versus functions that do have side effects, either because they pull variables from the global scope or receive parameters by reference and change them. You learned that you can call functions by their name or as callables stored in variables, anonymously or by name. Hopefully, you have got a taste of how flexible and powerful functions are and how they can help you to write robust code by enforcing strict types.

In the next chapter, you will learn how to combine constants, variables, and functions that belong together logically...