Creating a module

When you start working on a new project, the first thing to do is to create a module for it. A module is how Go manages dependencies.

How to do it...

1. Create a directory to store a new module.
2. Under that directory, use go mod init <moduleName> to create the new module. The go.mod file marks the root directory of a module. Any package under this directory will be a part of this module unless that directory also has a go.mod file. Although such nested modules are supported by the build system, there is not much to be gained from them.
3. To import a package in the same module, use moduleName/packagePath. When moduleName is the same as the location of the module on the internet, there are no ambiguities about what you are referring to.
4. For the packages under a module, the root of the module is the closest parent directory containing a go.mod file. All references to other packages within a module will be looked up in the directory tree under the module root.
5. Start by creating a directory to store the project files. Your current directory can be anywhere on the filesystem. I have seen people use a common directory to store their work, such as $HOME/projects (or \user\myUser\projects in Windows). You may choose to use a directory structure that looks like the module name, such as $HOME/github.com/mycompany/mymodule (or \user\myUser\github.com\mycompany\mymodule in Windows). Depending on your operating system, you may find a more suitable location.

Warning

Do not work under the src/ directory of your Go installation. That is the source code for the Go standard library.

Tip

You should not have an environment variable, GOPATH; if you have to keep it, do not work under it. This variable was used by an older mode of operation (Go version <1.13) that is now deprecated in favor of the Go module system.

Throughout this chapter, we will be using a simple program that displays a form in a web browser and stores the entered information in a database.

After creating the module directory, use go mod init. The following commands will create a webform directory under projects and initialize a Go module there:

$ cd projects
$ mkdir webform
$ go mod init github.com/examplecompany/webform

This will create a go.mod file in this directory that looks like this:

module github.com/PacktPublishing/Go-Recipes-for-Developers/chapter1/webform
go 1.21.0

Use a name that describes where your module can be found. Always use a URL structure such as the <host>.<domain>/location/to/module format (e.g., github.com/bserdar/jsonom). In particular, the first component of the module name should have a dot (.) (the Go build system checks this).

So, even though you can name the module something such as webform or mywork/webform, do not do so. However, you can use something such as workspace.local/webform. When in doubt, use the code repository name.