Does it make sense to have two packages in the same directory?

44
votes

I have a project that provides a library (exports some funcs) and also must provide a command-line interface (there must be an executable file).

Example of directory structure:

whatever.io/
    myproject/
        main.go
        myproject.go

The go compiler needs the package main and func main to start execution. My library needs the package myproject where I put stuff on it. This is what the go tool says when I am building another project that tries to import myproject:

main.go:5:2: found packages myproject (myproject.go) and main (main.go) in $GOPATH/src/whatever.io/myproject

So I believe there is no way to do it.

Should I move the library or the CLI to another package?

4
gopackage

4 Answers

30
votes

Just move your packages inside a new folder within the same directory of main.go. Remember to import the new package from the reference of the $GOPATH.

Example:

user@user:~/p/go/test/so-multipack$ ls -R
.:
a  main.go

./a:
a.go
user@user:~/p/go/test/so-multipack$ cat main.go 
package main

import (
    "../so-multipack/a"
)
func main(){
    a.Hello()
}
user@user:~/p/go/test/so-multipack$ cat a/a.go 
package a
import (
    "fmt"
)
func Hello(){
    fmt.Println("hello from a")
}
user@user:~/p/go/test/so-multipack$ go run main.go 
hello from a
user@user:~/p/go/test/so-multipack$ go build 
user@user:~/p/go/test/so-multipack$ ls
a  main.go  so-multipack
user@user:~/p/go/test/so-multipack$

Useful link:

go build vs go build file.go

24
votes

You cannot have two packages per directory, hence the error. So the solution as @Larry Battle said to move your myproject.go to a new directory.

From How to write go code

Go code must be kept inside a workspace. A workspace is a directory hierarchy with three directories at its root:

src contains Go source files organized into packages (one package per directory),

pkg contains package objects, and

bin contains executable commands.

7
votes

In most cases, no. However, there is an exception for unit tests.

Working Example:

Here are 2 different packages (mypackage and mypackage_test) in 1 directory (mypackage). The compiler will not complain about this.

mypackage folder:

mypackage/
  foo.go
  foo_test.go

mypackage/foo.go:

package mypackage

func Add(a int, b int) int {
    return a + b
}

mypackage/foo_test.go:

package mypackage_test

// Unit tests...

Rules:

  1. The 2 packages must have the following names:

    • NameOfDirectory.
    • NameOfDirectory + _test.

  2. The names of the files in the _test package must end with _test.go

If you're receiving a confusing compiler error along the lines of found packages "foo" and "bar", you've probably broken one or more of these rules.

2
votes

You can't have two golang files in one directory with two packages. So you need to move main.go out of myproject.

the directory structure before move

whatever.io/
    go.mod
    myproject/
        main.go
        myproject.go

After move

whatever.io/
    go.mod
    main.go
    myproject/
        myproject.go

And you need to change your main.go's import path. If the module name is aaa

Before

import "aaa"

Need change to this

import "aaa/myproject"