Documentation on golang packages and import syntax

[Daryl Robert Miller]

I have created local packages in support of my main golang program; it has been challenging to figure out where to put these packages and how to import them.  Obviously this area of Go has changed over the years so some examples out there are just wrong.  I got things working but can find no info on why, so my question is where is an explaination of how / why the below works (specifically using "main" prefix):

go version go1.16.5 darwin/amd64

Using Visual Studio Code v 1.58.0 on MacOS

~/go/src/myproject/main.go

package main

import "main/mypackage"

func main() {

    mypackage.Dothis()

}

---

~/go/src/myproject/mypackage/mypackage.go

package mypackage

func Dothis() { }

[Shulhan]

Hi Daryl,

On Sat, 10 Jul 2021 12:12:41 -0700 (PDT)
Daryl Robert Miller <dar...@uci.edu> wrote:

> I have created local packages in support of my main golang program;
> it has been challenging to figure out where to put these packages and
> how to import them. Obviously this area of Go has changed over the
> years so some examples out there are just wrong.

The official Go website provides two up-to-date examples on how create
package and to import them,

* https://golang.org/doc/code
* https://golang.org/doc/tutorial/create-module

All of them now include creating and using package as part of the Go
module.

> I got things
> working but can find no info on why, so my question is where is an
> explaination of how / why the below works (specifically using "main"
> prefix):

The specification for packages and import can be read on this pages:

* https://golang.org/ref/spec#Packages,
* https://golang.org/ref/spec#Import_declarations

>
> go version go1.16.5 darwin/amd64
> Using Visual Studio Code v 1.58.0 on MacOS
>

> *~/go/src/myproject/main.go*

> package main
>
> import "main/mypackage"
>
> func main() {
> mypackage.Dothis()
> }
> ---
>

> *~/go/src/myproject/mypackage/mypackage.go*
> package mypackage
>
> func Dothis() { }
>
>

Assuming that you are not enabling Go module, anything under
"$HOME/go/src/" directory will be considered as importable.

So, if you have "myproject/mypackage", where "myproject" defined as
package "main", then "main/mypackage" is the _import path_ for that
package that can be imported by any Go source code under "$HOME/go/src"
except by the package itself.

--
Shulhan

[Brian Candler]

On Sunday, 11 July 2021 at 10:21:53 UTC+1 Shulhan wrote:

Assuming that you are not enabling Go module, anything under
"$HOME/go/src/" directory will be considered as importable.

But you really, really SHOULD be using module mode.  You soon may not have any choice:

https://blog.golang.org/go116-module-changes#TOC_2.

(although that change is now not going to be made for 1.17)

It's only one extra command to type:

go mod init example.com/myprog

(you can use whatever you like for the module name, if you're not planning on publishing it).  That creates go.mod in the current directory.  Then you can use

import "example.com/myprog/foo"

and it'll get the package from ./foo/ relative to where the go.mod file sits.

Example:

https://play.golang.org/p/YQoAu1Iwkor

[Daryl Miller]

Thanks!