Refactor Go Package by Using gomvpkg

https://blog.golang.org/gopher

Go provides a lot of tools to help Go developers. They help Go developers to be productive when they are trying to solve their problems with Go. You can see the list of tools at https://godoc.org/golang.org/x/tools

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I've seen many developers that moved from other technology stacks (Java Spring, Ruby on Rails, etc.) use the previous project structure from those to Go project. Layer-based is the one example (controller, model, service, common, util, repository, etc.). In Go, mostly, we will not do that. When we design a Go package (structure), we think about what it provides, not what it contains. And how we use them. You can read my blog about Go Package (Structure) Design

As you may know, it is painful when you are trying to refactor legacy Go package. Especially, packages like common, util, base. Because it has been used around the project (other packages use them by importing). If you refactor those packages, you need to put a lot of effort to change the import path in every derived package.

Actually, there is a Go tool for this situation. It is gomvpkg.https://godoc.org/golang.org/x/tools/cmd/gomvpkg

I'm going to show you how to refactor legacy Go package by using gomvpkg. We have the package common/consumer.

	package event
	import "github.com/ballweera/play-gomvpkg/common/consumer"
	func Process() {
	consumer.Consume()
	}

view raw event.go hosted with ❤ by GitHub

	package main
	import (
	"github.com/ballweera/play-gomvpkg/common/consumer"
	"github.com/ballweera/play-gomvpkg/event"
	)
	func main() {
	consumer.Consume()
	event.Process()
	}

view raw main.go hosted with ❤ by GitHub

You can see that github.com/ballweera/play-gomvpkg/common/consumer has been used in only two places (event.go and main.go). But in a large program, it may be used more than 10 or 20 times. So it is a bit difficult to refactor and take time to refactor them.

By using gomvpkg, we can execute only one command to change from github.com/ballweera/play-gomvpkg/common/consumer to github.com/ballweera/play-gomvpkg/kafka

	gomvpkg -from github.com/ballweera/play-gomvpkg/common/consumer -to github.com/ballweera/play-gomvpkg/kafka

view raw gomvpkg hosted with ❤ by GitHub

After executing gomvpkg, you would see the result like this

	package event
	import "github.com/ballweera/play-gomvpkg/kafka"
	func Process() {
	kafka.Consume()
	}

view raw event.go hosted with ❤ by GitHub

	package main
	import (
	"github.com/ballweera/play-gomvpkg/event"
	"github.com/ballweera/play-gomvpkg/kafka"
	)
	func main() {
	kafka.Consume()
	event.Process()
	}

view raw main.go hosted with ❤ by GitHub

Now, in event.go and main.go, the import path is changed to github.com/ballweera/play-gomvpkg/kafka.

One thing you need to know about gomvpkg. It could not be run outside GOPATH. So you need to move your Go project to GOPATH before using it. And if you use Go Module (go.mod), you also need to set GO111MODULE=auto.

I already created the repo to play the gomvpkg https://github.com/ballweera/play-gomvpkg.

Have fun!!