Project Organization and Style

Internal Boundaries

The internal directory gives Go projects an import boundary enforced by the toolchain.

internal packages Model internal imports explicitly so package boundaries stay visible.

Internal Boundaries

importPath
internal_boundaries.go
Replay: real traced execution (multi-file project)
package main

import (
	"fmt"
	"strings"
)

func main() {
	var importPath = "example.com/shop/internal/config"
	ownedPrefix := "example.com/shop/"
	usesInternal := strings.Contains(importPath, "/internal/")
	owned := strings.HasPrefix(importPath, ownedPrefix)
	allowed := !usesInternal || owned

	fmt.Println("import=", importPath)
	fmt.Println("uses_internal=", usesInternal)
	fmt.Println("owned_prefix=", owned)
	fmt.Println("allowed=", allowed)
}

package main

import (
	"fmt"
	"strings"
)

func main() {
	var importPath = "example.com/shop/pkg/config"
	ownedPrefix := "example.com/shop/"
	usesInternal := strings.Contains(importPath, "/internal/")
	owned := strings.HasPrefix(importPath, ownedPrefix)
	allowed := !usesInternal || owned

	fmt.Println("import=", importPath)
	fmt.Println("uses_internal=", usesInternal)
	fmt.Println("owned_prefix=", owned)
	fmt.Println("allowed=", allowed)
}

package main

import (
	"fmt"
	"strings"
)

func main() {
	var importPath = "example.com/other/internal/config"
	ownedPrefix := "example.com/shop/"
	usesInternal := strings.Contains(importPath, "/internal/")
	owned := strings.HasPrefix(importPath, ownedPrefix)
	allowed := !usesInternal || owned

	fmt.Println("import=", importPath)
	fmt.Println("uses_internal=", usesInternal)
	fmt.Println("owned_prefix=", owned)
	fmt.Println("allowed=", allowed)
}

  1. importPath ← "example.com/shop/internal/config", ownedPrefix ← "example.com/shop/"

    8func main() {9  var importPath→ "example.com/shop/internal/config" = "example.com/shop/internal/config" //@importPath="example.com/shop/pkg/config", "example.com/other/internal/config"10  ownedPrefix→ "example.com/shop/" := "example.com/shop/"11  usesInternal→ true := strings.Contains(importPath"example.com/shop/internal/config", "/internal/")12  owned→ true := strings.HasPrefix(importPath"example.com/shop/internal/config", ownedPrefix"example.com/shop/")13  allowed→ true := !usesInternaltrue || ownedtrue1415  fmt.Println("import=", importPath"example.com/shop/internal/config")16  fmt.Println("uses_internal=", usesInternaltrue)17  fmt.Println("owned_prefix=", ownedtrue)18  fmt.Println("allowed=", allowedtrue)19}
    outputimport= example.com/shop/internal/config
uses_internal= true
owned_prefix= true
allowed= true

  1. importPath ← "example.com/shop/pkg/config", ownedPrefix ← "example.com/shop/"

    8func main() {9  var importPath→ "example.com/shop/pkg/config" = "example.com/shop/pkg/config"10  ownedPrefix→ "example.com/shop/" := "example.com/shop/"11  usesInternal→ false := strings.Contains(importPath"example.com/shop/pkg/config", "/internal/")12  owned→ true := strings.HasPrefix(importPath"example.com/shop/pkg/config", ownedPrefix"example.com/shop/")13  allowed→ true := !usesInternalfalse || ownedtrue1415  fmt.Println("import=", importPath"example.com/shop/pkg/config")16  fmt.Println("uses_internal=", usesInternalfalse)17  fmt.Println("owned_prefix=", ownedtrue)18  fmt.Println("allowed=", allowedtrue)19}
    outputimport= example.com/shop/pkg/config
uses_internal= false
owned_prefix= true
allowed= true

  1. importPath ← "example.com/other/internal/config", ownedPrefix ← "example.com/shop/"

    8func main() {9  var importPath→ "example.com/other/internal/config" = "example.com/other/internal/config"10  ownedPrefix→ "example.com/shop/" := "example.com/shop/"11  usesInternal→ true := strings.Contains(importPath"example.com/other/internal/config", "/internal/")12  owned→ false := strings.HasPrefix(importPath"example.com/other/internal/config", ownedPrefix"example.com/shop/")13  allowed→ false := !usesInternaltrue || ownedfalse1415  fmt.Println("import=", importPath"example.com/other/internal/config")16  fmt.Println("uses_internal=", usesInternaltrue)17  fmt.Println("owned_prefix=", ownedfalse)18  fmt.Println("allowed=", allowedfalse)19}
    outputimport= example.com/other/internal/config
uses_internal= true
owned_prefix= false
allowed= false