Here is a brief tutorial for those new to Go Module. This is by no means a comprehensive guide to Go Module, but I hope this should be enough to get you started.
What is Go Module, and why you should be using one? Go Module is a dependency management tool. The primary benefit of Go Module is that it allows you to specify specific versions of your dependencies. That way you can ensure your project does not break when some of your dependencies change their APIs. Compare this with GOPATH that always assume you want to use the latest versions of your dependencies. The other benefit of Go Module is that you can set up your projects outside of your GOPATH folder structure. If you are migrating existing GOPATH projects into Go Module, you will save a lot of headache by moving them out of your GOPATH folder. Next, we need to understand versioning. A version is normally written as v1.2.3 where 1 is the major number, 2 is the minor number, and 3 is the patch number. The general convention adopted by Go community is that you should increase the major number if there is a breaking change. Increase the minor number, if you are adding new features. Increase the patch number for bug fixing. Understanding this versioning convention is important so that you know what to expect when you specify your dependency's version, and to keep your library compatible with everyone else's expectation. Go Module is just a configuration file inside your project called *go.mod* that specifies other go tools what to do with your projects. Go build tools usually create another file (*go.sum*) but you normally do not need to mess with this. If you accidentally deleted go.sum, your project will still build just fine as long as your go.mod is there. You can manually edit your go.mod, but for the purpose of this guide, I will stick to using tools whenever possible, because it is easier. To create a Go Module, step inside your project folder, and type *go mod init <namespace> *where <namespace> is the qualified name of your project. For instance, if you want to call your project "github.com/henry/myproject", then inside your myproject folder, type *go mod init github.com/henry/myproject* To add a dependency, just code away as you normally would. Every time you build, go build tools will examine your import lines and automatically add those dependencies into your go.mod. If your dependency is stored somewhere else that Go tools can't find (eg. in your local computer), you need to manually specify where to find it. Use *go mod edit -replace <name>=<path>*, where <name> is the qualified name of your dependency and <path> is where it is located. To upgrade your dependencies, you can issue *go get -u all* command, or use *go get -u <pkg>* to upgrade a specific package. There are also third party tools to help check for outdated dependencies. To version your project, simply add a tag in your git commit and upload your project. Go Module will recognize this. For instance, if you want to commit your project to version 0.2.0, simply add tag "v0.2.0" to your commit. This applies to major version number 0 and 1. For major version number 2 (eg. v2.0.0) upwards, see below. For version major 2 upwards, instead of simply tagging your commit as usual, you need a special project structuring. For version 2.0.0, add folder v2 into your project. If your are upgrading into major version 3, add folder v3, and so on. Assuming we use the above *github.com/henry/myproject*, now add v2 folder so that it becomes *myproject/v2. *Inside the v2 folder, start a new go mod. In our example, you would type *go mod init github.com/henry/myproject/v2* . Note the v2 in the end. Add your version 2 stuffs into the v2 folder and code away as usual, commit, tag and upload. Now if you want to use your version 2 library in your other projects, simply change your import lines to include the v2. So, in our example, change your import line from "github.com/henry/myproject" to "github.com/henry/myproject/v2". Go build tools will recognize this and automatically use the version 2 of your library. Note that you can always manually edit your go.mod. For further reading, see Using Go Modules <https://blog.golang.org/using-go-modules> I hope this helps. Henry -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/3fe73178-52f7-4da9-b1bd-5170e1882ffd%40googlegroups.com.
