Implement simple containerOf in Golang

containerOf

package main

import (
	"fmt"
	"unsafe"
)

// the dummy struct
type B struct {
	dummy int
}

// the dummy container
type A struct {
	foo string
	B
	D string
}

func (this *B) ContainerA() A {
	return *(*A)((unsafe.Pointer)((uintptr(unsafe.Pointer(this)) - unsafe.Offsetof(A{}.B))))
}

func main() {
	a := A{"foo", B{}, "hehe"}
	b := &(a.B) // the b must be a pointer
	fmt.Println(b.ContainerA())
}