Learning Go

Chapter 9. Modules, Packages, and Imports

Most modern programming languages have a system for organizing code into namespaces and libraries, and Go is no exception. As we’ve seen while exploring other features, Go introduces some new approaches to this old idea. In this chapter, we’ll learn about organizing code with packages and modules, how to import them, how to work with third-party libraries, and how to create libraries of your own.

Repositories, Modules, and Packages

Library management in Go is based around three concepts: repositories, modules, and packages. A repository is familiar to all developers. It is a place in a version control system where the source code for a project is stored. A module is the root of a Go library or application, stored in a repository. Modules consist of one or more packages, which give the module organization and structure.

Note

While you can store more than one module in a repository, it isn’t encouraged. Everything within a module is versioned together. Maintaining two modules in one repository means tracking separate versions for two different projects in a single repository.

Before we can use code from packages outside of the standard library, we need to make sure that we have declared that our project is a module. Every module has a globally unique identifier. This is not unique to Go. Java uses globally unique package declarations like com.companyname.projectname.library.

In Go, we usually use the path to the module repository ...