如何使用嵌套目录进行构建

Question

In the process of learning go I was playing around with making my own libraries. Here is what I did: in my $GOPATH/src I have two folders: mylibs and test. The test folder has a file called test.go which contains

package test

import "mylibs/hi/saysHi"

func main() {
    saysHi.SayHi()
}

The mylibs folder contains another folder called hi, which has a file called saysHi.go containing:

package saysHi

import "fmt"

func SayHi() {
    fmt.Printf("Hi
")
}

So the directory structure looks like this:

• GOPATH/src
• • test
• • • test.go
• • mylibs
• • • hi
• • • • saysHi.go

The problem is that when I try to compile test it complains saying

cannot find package "mylibs/hi/saysHi" in any of: 
    [...]
    $GOPATH/src/mylibs/hi/saysHi (from $GOPATH)

I have deliberately made the directory structure deeper than necessary. If I make a simpler directory structure where I place saysHi.go in $GOPATH/saysHi/saysHi.go then it works.

But I don't see a reason for why this wouldn't work. Any ideas?

Answer 1

Generally speaking, your directory name should match the package name. So if you define

package saysHi

and want to import it with

import "mylibs/hi/saysHi"

you should place it in a structure like this:

• mylibs
• • hi
• • • saysHi
• • • • saysHi.go

The name of the .go file(s) inside the package makes no difference to the import path, so you could call the .go file anything you like.

To explain it a bit further, the import path you use should be the name of the directory containing the package. But, if you define a different package name inside that directory, you should use that name to access the package inside the code. This can be confusing, so it's best to avoid it until you understand where it's best used (hint: package versioning).

It gets confusing, so for example, if you had your package in the path

• mylibs
• • hi
• • • saysHi.go

And inside saysHi.go defined,

package saysHi

Then in test.go you will import it with

import "mylibs/hi"

And use it with

saysHi.SayHi()

Notice how you import it with the final directory being hi, but use it with the name saysHi.

Final note

Just in case you didn't know the following: your test file is called test.go, and that's fine, if it's just as an example, and not an actual test file for saysHi.go. But if it is/were a file containing tests for saysHi.go, then the accepted Go standard is to name the file saysHi_test.go and place it inside the same package alongside saysHi.go.

One more final note

I mentioned how you are allowed to choose a different package name from the directory name. But there is actually a way to write the code so that it's less confusing:

 import (
    saysHi "mylibs/hi"
 )

Would import it from the mylibs/hi directory, and make a note of the fact that it should be used with saysHi, so readers of your code understand that without having to go look at the mylibs/hi code.