Go Multimodule

Let's use go.work to configure for multimodule workspace in Go project created here

At the moment, the directory structure for the root file fourier, is as below

            $ ls *
go.mod  main.go

hello:
go.mod          hello.go
$
          

The file contents are as below, in the file hello/hello.go in the folder hello

package hello

import (
    "fmt"
    "runtime"	
)

func SayArch() string {
    arch := fmt.Sprintf("Architecture: %s", runtime.GOOS)
    return arch
}

In the root file, main.go in the root folder, fourier:

package main

import (
    "fmt"
    "example.com/fourier/hello"
)

func main () {
    fmt.Println("Hello world")
    arch := hello.SayArch()
    fmt.Println(arch)
}

And the go.mod file contents in the root folder, fourier:

            $ cat go.mod 
module example.com/fourier

go 1.18
$
          

The go.mod file contents in the hello package

            $ cat hello/go.mod 
module example.com/fourier/hello

go 1.18
$
          

Initialize the workspace

Let's create the go.work file to specify a workspace with the module. go work init command tells go to create a go.work file for a workspace containing the modules in the . and the ./hello directories.

Note that trying to run it with go.work not initialized leads to the local module hello not being found

            $ go run .
main.go:5:2: no required module provides package example.com/fourier/hello; to add it:
        go get example.com/fourier/hello
$ go work init . ./hello 
$ ls
go.mod  go.work hello   main.go
$ cat go.work 
go 1.18

use (
        .
        ./hello
)
$ go run .
Hello world
Architecture: darwin
$
          

Package main from its main folder

Let's take into account the fact that main.go now exists not in root folder, fourier, but in a folder within root, main

            $ pwd
/Users/siliconSavanna/Projects/Golang/fourier 
$ mkdir main
$ mv main.go ./main
$ cd main 
$ go mod init example.com/fourier/main
go: creating new go.mod: module example.com/fourier/main
go: to add module requirements and sums:
        go mod tidy
$
          

So there are two ways to go about this:

Add the main and hello directories while initializing the go.work file

            $ cd ../
$ pwd
/Users/siliconSavanna/Projects/Golang/fourier 
$ rm go.work 
$ go work init ./main ./hello 
$ cat go.work                
go 1.18

use (
        ./hello
        ./main
)
$ go run main/main.go        
Hello world
Architecture: darwin
$
          

Use go mod edit -replace

            $ cd ../
$ pwd
/Users/siliconSavanna/Projects/Golang/fourier 
$ rm go.work 
$ cd main 
$ go mod edit -replace example.com/fourier/hello=../hello
$ go mod tidy
go: found example.com/fourier/hello in example.com/fourier/hello v0.0.0-00010101000000-000000000000
$ go run .
Hello world
Architecture: darwin
$
          

For the latter, the state of the go.mod file in main folder becomes

            $ cat go.mod 
module example.com/fourier/main

go 1.18

replace example.com/fourier/hello => ../hello

require example.com/fourier/hello v0.0.0-00010101000000-000000000000
$
          

To Go and Beyond!