2022-05-01：golang里，结构体B里包含一个结构体A和一个整型成员变量。现在要给结构体A实现一个方法，让它能访问到B

package main

import (
  "fmt"
  "unsafe"
)

type A struct {
  i1 int
  s1 string
}

//直接把B传进来
func (this *A) GetInt1(b1 *B) int {
  return b1.Int
}

//已知偏移量
func (this *A) GetInt2() int {
  b1 := (*B)(unsafe.Pointer(uintptr(unsafe.Pointer(this)) - 8))
  return b1.Int
}

//未知偏移量
func (this *A) GetInt3() int {
  b := new(B)
  offset := uintptr(unsafe.Pointer(&b.a1)) - uintptr(unsafe.Pointer(b))

  b1 := (*B)(unsafe.Pointer(uintptr(unsafe.Pointer(this)) - offset))
  return b1.Int
}

type B struct {
  Int int
  a1  A
}

func main() {
  b1 := new(B)
  b1.Int = 55
  fmt.Println(b1.a1.GetInt1(b1))
  fmt.Println(b1.a1.GetInt2())
  fmt.Println(b1.a1.GetInt3())
}