Learning Go, 2nd Edition

Chapter 10. Modules, Packages, and Imports

Most modern programming languages have a system for organizing code into namespaces and libraries, and Go is no exception. As you’ve seen while exploring other features, Go introduces some new approaches to this old idea. In this chapter, you’ll learn how to organize 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 a bundle of Go source code that’s distributed and versioned as a single unit. Modules are stored in a repository. Modules consist of one or more packages, which are directories of source code. Packages give a module organization and structure.

Note

While you can store more than one module in a repository, it is discouraged. Everything within a module is versioned together. Maintaining two modules in one repository requires you to track separate versions for two different modules in a single repository.

Unfortunately, different programming languages use these words to represent different concepts. While packages in Java and Go are similar, a Java repository is a centralized place to store multiple artifacts (the analogue of a Go module). Node.js and Go swap the meanings ...