How to Build a GO Library without a main

I'm a seasoned developer but new to GO. The documentation I have found is not straightforward. I'm used to Java, Scala and Python, but GO is new to me. I'm trying to create a library in GO, and I'm in the first steps of creating the project structure. When I run go build it tells me there are "no GO files in ...". This is a pure library and I don't want a main file. Is there a way to achieve this or is a main file required no matter what?

Finding documentation and looking at sample projects.
Edit. I do have files and I have run some tests with a main file in place. But as soon as I delete the main file it's when I get a bit lost on how to build it correctly.

It depends a bit on what you mean by "library". If you mean a pre-compiled binary object, like a .a or .so library in C, Go doesn't really have anything like that. Dependent packages are downloaded as source and then compiled into your binary.

If you mean, "a module I can import and use in other projects"...Have you looked to see how other modules are structured? Using e.g. the yaml module as an example, we see:

• There is no main.go
• If you clone it and run go mod tidy; go build the go build command will run without errors.

So for example I can create a module mymodule-dep with this structure:

.
├── functions.go
└── go.mod

Where go.mod has:

module github.com/larsks/mymodule-dep

go 1.20

And functions.go has:

package mymodule_dep

import "strings"

func Replace(s string) string {
	return strings.Replace(s, "Hello", "Goodbye", -1)
}

I can use that module by importing into another project, like this:

package main

import (
	"fmt"
	dep "github.com/larsks/mymodule-dep"
)

func main() {
	fmt.Println(dep.Replace("Hello, world!"))
}

This assumes that there exists a repository <https://github.com/larsks/mymodule-dep> (which does exist right now).

If I build the above code, running it produces:

Goodbye, world!

Usually you do not need to build your GO libraries.

You create library as GO files, test it and publish sources to GitHub. Published code has versions in Git (typically GitHub) and client can pick what version of library to use.

The client application that uses that library has a main.go file, and that is where you run go build command.

Go does not have an intermediate format like Java or .NET and also do not use libraries in binary executable format. Instead, GO uses dependencies in the form of GO code. That is similar to Node and Python, except, Go compiles final code and do not interpret it.