What is a package?

Go follows the Don’t Repeat Yourself (DRY) principle. This means that you should not write the same code twice. Refactoring your code into functions is the first step of the DRY principle. What if you had hundreds or even thousands of functions that you used regularly? How would you keep track of all those functions? Some of those functions might even have common characteristics. You could have a group of functions that perform math operations, string manipulations, printing, or file-based operations. You may be thinking of breaking them up into individual files:

Figure 10.3: Group functions by files

That could alleviate some of the issues. However, what if your string’s functionality started to grow further? You would then have a ton of string functions in one file or even multiple files. Every program you build would also have to include all of the code for string, math, and io. You would be copying code to every application...