Go: Developing local golang module

Tags: #go #dependencies

Developing local golang module.md

Copied verbatim from https://brokencode.io/how-to-use-local-go-modules-with-golang-with-examples/ so all credit goes to that author. I’m just gisting this content for my own future reference so I don’t have to go locate it again.

Importing local modules in main.go

So first we simply have to convert all of our directories into go modules. For that we need to add a go.mod at the root of every directories. Then inside of that go.mod give them whatever name that we want as module name. but bear in mind that it has to be an url. In my example I put this:

module example.org/hello in the go.mod for the hello directory module example.org/utils in the go.mod for the utils directory

The import makes a bit more sense now huh ? but we are not done yet.

The replace keyword

This is where the magic happens, go.mod files have a few keywords that can be very useful, one of them is replace what replace does is that it takes a module path (eg : example.org/hello) and replaces it with a direct or relative path.

here’s the syntax for the replace keyword :

replace url.com/of/the/module => /direct/path/to/files

Note that replace also works with relative paths.

The main go.mod

module example.com/localmodexample

go 1.13

require (
   example.org/hello v0.0.0
   example.org/utils v0.0.0

)

replace (
   example.org/hello => ./hello
   example.org/utils => ./utils
)

Usually go module dependencies work with versions, so to use local go modules with golang you have to set v0.0.0

Finally after the require, I just tell the compiler that those urls are local and can be found in the same directory under ./hello and ./utils. The great thing about this main go.mod file is that now even the utils module will know where to find the hello module because the url have been replaced.