Create a module meant for sharing

In this chapter, we will cover how you can create a module you can share with others.

Introduction

This chapter will cover:

Creating a project.
Testing the module locally.
Tag the module with different versions.
Try consuming the module as an external library.

Create a module

When you build a module meant for sharing, there’s some gotchas:

You need to create a package.
Your package won’t be called main.
There’s the concept of public and private parts of your code.
You can test it locally.
Upload your package to GitHub for wide distribution.

To create a module meant for wider use you need to first initialize a module.

Create a directory logger for your new package:
```
mkdir logger
cd logger   
```
Run go mod init <address at github>, for example:
```
go mod init github.com/softchris/logger
```
This will create a go.mod file in your directory.
```
logger/
  go.mod
```
The file looks like so:
```
module github.com/softchris/logger

go 1.16
```
It contains the package name and the version of Go it means to use.
Create a file to host your package code, for example log.go and give it the following content:
```
 package logger

 import (
  "fmt"
 )
    
 var Version string = "1.0"
    
 func Log(mess string) {
  fmt.Println("[LOG] " + mess)
 }
```
- Note package logger instead of main.
- The uppercase variables and methods makes the publicly available. Anything named with lowercase will be private for the package.

Test it locally

You can test your package locally. To do so you need a separate package that you can import your package from.

Move up a directory:
```
cd ..
```
Create a new directory logger-test:
```
mkdir logger-test
cd logger-test
```
Create a package, it will be used for testing only:
```
go mod init logger-test
```
Create a file main.go and add the following code:
```
 package main

 import "github.com/softchris/logger"
    
 func main() {
  logger.Log("hey there")
 }
```
At this point, you are consuming the “logger” package but it’s pointing to GitHub and your package doesn’t live there yet. However, you can repoint to a local address on your machine, let’s do that next.

Open go.mod and add the following:

require github.com/softchris/logger v0.0.0

replace github.com/softchris/logger => ../logger

Two things are happening here:

you are asking for the “logger” package:

 require github.com/softchris/logger v0.0.0

you are making it point to your local system instead of GitHub
```
 replace github.com/softchris/logger => ../logger
```

Run the package with go run:
```
 go run main.go
```
You should see:
```
 [LOG] hey there
```

Publish a package

To publish your package, you can put it on GitHub.

Create a git repo with git init:
```
git init
```
Create the repo on GitHub.

Make you do at least one commit:

 git add .
 git commit -m "first commit"

Do the following to upload your package to GitHub:

git remote add origin https://github.com/softchris/logger.git

git branch -M main
git push -u origin main

Tag your package with git tag:
```
git tag v0.1.0
git push origin v0.1.0
```
Now your package has the tag 0.1.0

Test it out

Go to your project “logger-test”:
```
cd ..
cd logger-test
```

Open up go.mod and remove these lines:

require github.com/softchris/logger v0.0.0

replace github.com/softchris/logger => ../logger

Run go mod tidy, this will force Go to go look for the package:

Your go.mod should now contain:

require github.com/softchris/logger v0.1.0

Also, your go.sum should contain:

github.com/softchris/logger v0.1.0 h1:Kqw7t9C3Y7BtHDLTx/KXEqHy5x8EJxrLian742S0di0=

github.com/softchris/logger v0.1.0/go.mod h1:rrzWjMsM3tqjetDBDyezI8mFCjGucF/b5RSAqptKF/M=

Run the program with go run:
```
go run main.go
```
You should see:
```
[LOG] hey there
```

Challenge

See if you can add a feature to your new package. Give it a new tag via Git. Then ensure your app is using this new version.