It is frustrating using Go Module for new Goer. This guide will not talk about too much how does Go find the package/modules but will show you step-by-step how to create and test a module in a Windows system.

Assumption

Go version >= 1.16
Go is set up on your laptop
I use folder F:\dev\golang\go_basic\moduledemo for testing
gitbash as terminal

Step-by-Step Guide

Enable module mode

# Check if go module mode
$ go env | grep GO111MODULE
set GO111MODULE=auto
# or
go env GO111MODULE

# If the value is off, plz use the gitbach command to set it to auto or on
export GO111MODULE=auto
export GO111MODULE=on

# For cmd.exe, kindly use set
set GO111MODULE=on
echo %GO111MODULE%

# Or use go command
go env -w GO111MODULE=on
go env GO111MODULE=on

Create a project folder, init module

# Create a new project folder at any place
mkdir moduledemo
cd moduledemo

# init the module with name moduledemo at the folder
go mod init moduledemo

Create the test source

$ tree
.
|-- boo
|   `-- Boo.go   => this is module, called by main.go
|-- go.mod       => this file is created via go mod init
`-- main.go

Source Code

main.go

package main

import (
    "fmt"
    "moduledemo/boo"
)

func main() {
    boo.Boo()
    fmt.Println("this msg is from main")
}

Boo.go

package boo

import "fmt"

func Boo() {
    fmt.Println("this msg is from boo module")
}

go.mod

module moduledemo

go 1.20

Use Go Module Step By Step Guide