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I'm writing small app following http://golang.org/doc/code.html

My directory tree looks like

-blog
  -bin
  -pkg
  -src
    -github.com
      -packages_that_i_imported
    -myblog
      -config
        routes.go
      server.go

my server.go file contains following code

package main

import "..." //ommited imports


func main(){
    r:= mux.InitRoutes()  //function from imported package
    Register_routes(r)  //function from routes.go
}

And my routes.go

package main

func Register_routes(r *Router){
  r.addRoute("test", "test", "test)
}

But after I do go run server.go I'm getting following error

$ go run server.go 
# command-line-arguments
./server.go:10: undefined: Register_routes

GOPATH variable points to my /blog folder

What am I missing? Why go doesn't it see files in subdirectories?

P.S. config/routes.go is part of server.go package

P.P.S I have moved routes.go to the same folder as server.go, but the error is still present

In order to use a function defined in another package, first you have to import it:

import "myblog/config"

And after that you have to refer to it by the package name:

config.Register_routes(r)

Also the package name should reflect the folder name in which it is defined. In your routes.go the package should be config. Package main is special, the main package will be compiled into an executable binary (it is the entry point of the program). See Program Execution in the language specification.

From the page you linked: Package names:

Go's convention is that the package name is the last element of the import path: the package imported as "crypto/rot13" should be named rot13.

Executable commands must always use package main.

There is no requirement that package names be unique across all packages linked into a single binary, only that the import paths (their full file names) be unique.

Check out the blog post Package names for a detailed guideline.

Note that different files of the same package have to be put into the same folder. And different files of the same package can use everything from the package without importing it and without using the package name (doesn't matter in which file it is defined). This is also true for unexported identifiers. From another package you can only access exported identifiers (their name must start with a capital letter).

Also the go naming convention is to used mixed caps rather than underscores to write multiword names, see Effective Go / MixedCaps. So the function should be named RegisterRoutes but this is not a requirement.

From the documentation on the go command:

go run [build flags] [-exec xprog] gofiles... [arguments...]

Run compiles and runs the main package comprising the named Go source files.

You need to give the name of the second file to the go run command to include it.

go run server.go config/routes.go