Maybe private method with golang

test.go

package main

import (
	"fmt"
)

func main() {
	fmt.Printf("main() in test.go\n")
	new(Test).Hoge()
	Test2.Hoge()
	Test2.aaa() // compile error
}

type Test struct{}

func (t Test) Hoge() {
	fmt.Printf("Hoge() in test.go\n")
}

test2.go

package main

import "fmt"

type Test2Funcs interface {
	Hoge()
}

var Test2 Test2Funcs = test2Funcs{}

type test2Funcs struct{}

func (t test2Funcs) Hoge() {
	fmt.Printf("Hoge() in test2.go\n")
}

func (t test2Funcs) aaa() {
	fmt.Printf("aaa() in test2.go\n")
}

$ go run *.go
# command-line-arguments
./test.go:11:7: Test2.aaa undefined (type Test2Funcs has no field or method aaa)