How do packages work in golang

Question

I was trying to understand how packages work in go better in terms of what golang actually enforces rather than what is usually done or considered good practice (we can talk about good practice later too, but I wish to understand go first).

From effective go it says:

"Another convention is that the package name is the base name of its source directory..."

However, the description above doesn't seem to be forced by go or required. Thus, I was wondering, if I was allowed to have multiple files with different package declarations at the top in the same directory base. If I am allowed to have multiple package declaration in the same directory, how do I then import them and use each one separately in the same file? Basically, I guess one of the problem I have is due to the wording of some of the go tutorial/documentation. If it is by convention, then for me, its implied that it is NOT enforced by the language. Because for example, go programmers do NOT write the keyword func for a function by convention. We write func because otherwise go will yell at you and it will not compile. Thus, I wish to clarify this with the example bellow (and if possible change the documentation for go, because this is a big deal in my opinion, how can this be done?).

For example say I have three file A.go, B.go, C.go that print a print function Print() that simply prints a,b,c respectively. They are all on the same base directory called maybe base. Then each has a different package declaration package Apkg, package Bpkg, package Cpkg.

how would you then go and import them? Would something as follow work?

package main

import(
    nameA "github.com/user_me/base/Apkg"
    nameB "github.com/user_me/base/Bpkg"
    nameC "github.com/user_me/base/Cpkg"
)

func main() {
    nameA.Print() \\prints a
    nameB.Print() \\prints b
    nameC.Print() \\prints c
}

or maybe we don't even need to specify the name if the package statments are the top are already different:

package main

import(
    "github.com/user_me/base"
)

func main() {
    Apkg.Print() \\prints a
    Bpkg.Print() \\prints b
    Cpkg.Print() \\prints c
}

the printing file are:

A.go:

//file at github.com.user_me/base and name A.go
package Apkg

import "fmt"

func Print(){
    fmt.Println("A")
}

B.go:

//file at github.com.user_me/base and name B.go
package Bpkg

import "fmt"

func Print(){
    fmt.Println("B")
}

C.go: //file at github.com.user_me/base and name C.go package Cpkg

import "fmt"

func Print(){
    fmt.Println("C")
}

Also, if you can have a name different from the base, could someone clarify to me how the import is actually done? If the package name is package Apkg in base does the import have to be import github.com/user_me/base or import github.com/user_me/base/Apkg or github.com/user_me/Apkg.

I have not yet tested this but I will do so soon. The importing deal in go has been a little confusing for me and would love to get an answer and share it with the world.

Answer 1

No, it's 1 package per folder, so you would have to have them :

$GOPATH/src/github.com/user_me/base/Apkg/a.go
$GOPATH/src/github.com/user_me/base/Bpkg/b.go
$GOPATH/src/github.com/user_me/base/Cpkg/c.go

You can't even build it otherwise:

┌─ oneofone@Oa [/t/blah]                                                                                                         
└──➜ go build
can't load package: package .: found packages pkgA (blah1.go) and pkgB (blah2.go) in /tmp/blah

Your your package name doesn't need to have the same name as the directory they are in, however all files in one directory must have the same package name.

Also, you can rename packages on import, for example:

import (
   cr "crypto/rand"
   mr "math/rand"
)

Or your library is called main (bad idea btw) :

import m "github.com/user_me/base/main"