Go Package Structure: Do We Need a `package.go` File, How to Import Internal Files, and Can We Access Types Across Files?

Go Language Package Structure: An in-Depth Explanation

When working with Go, adhering to established conventions is crucial. However, understanding these conventions is paramount before their effective implementation. This article tackles a frequently asked question regarding Go's package structure.

Question

Setup: Following the recommended project structure, we have:

$GOPATH/
  src/
    github.com/
      username/
        projectname/
          main.go
          numbers/
            rational.go
            real.go
            complex.go

main.go:

package main

import (
  "fmt"
  "./numbers"
)

func main() {
  fmt.Println(numbers.Real{2.0})
}

Questions:

• Do we require a package.go file in each package folder?
• How do we import files within the same package in numbers.go?
• Can we define types like Real in real.go and access them in main.go as fmt.Println(numbers.Real{2.0})?

Answer

1. package.go File

The assumption that every package directory requires a package.go file is incorrect. In Go, files within a single directory are automatically grouped into a package. Creating a package.go file is unnecessary.

2. Importing Files Within a Package

Go does not support importing files. Package numbers should be imported directly, rather than individual files like rational.go, real.go, and complex.go. In our example, remove the ./ prefix and use import "github.com/username/projectname/numbers".

3. Sharing Types

Types like Real should be defined in a file within the package, such as real.go. As the files belong to the same package, no additional import statement is needed. Accessing the Real type in main.go as fmt.Println(numbers.Real{2.0}) is correct.

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