Golang Module

~$ mkdir greetings
~$ cd greetings
~$ go mod init example.com/greetings

In a text editor, create greetings.go with the following content:

package greetings

import "fmt"

// Hello returns a greeting for the named person.
func Hello(name string) string {
    // Return a greeting that embeds the name in a message.
    message := fmt.Sprintf("Hi, %v. Welcome!", name)
    return message
}

Call it from another module

~$ cd ..
~$ mkdir hello
~$ cd hello
~$ go mod init example.com/hello

In a text editor, create hello.go with the following content:

package main

import (
    "fmt"

    "example.com/greetings"
)

func main() {
    // Get a greeting message and print it.
    message := greetings.Hello("Gladys")
    fmt.Println(message)
}

Edit example.com/hello module to use your local example.com/greetings module. Inside ‘hello’ directory:

~$ go mod edit -replace example.com/greetings=../greetings

Then, tidy it

~$ go mod tidy

The go.mod file in example.com/hello module should now be:

module example.com/hello

go 1.16

replace example.com/greetings => ../greetings

require example.com/greetings v0.0.0-00010101000000-000000000000

Then, from hello directory, run it.

~$ go run .
Hi, Gladys. Welcome!

NOTE: This example was directly taken from https://golang.org/doc/tutorial/create-module so check it there for further details.