GOLANG: Patching private fields with values

main.go

package main

import (
  redis "gopkg.in/redis.v3"
	"reflect"
	"unsafe"
	"fmt"
)

type A struct {
	val string
}

func (a *A) Val() string {
	return a.val
}

type B struct {
	val []string
}

func (b *B) Val() []string {
	return b.val
}

func change_val(f *A, v string) {
	pointerVal := reflect.ValueOf(f)
	val := reflect.Indirect(pointerVal)
	member := val.FieldByName("val")
	ptrToY := unsafe.Pointer(member.UnsafeAddr())
	realPtrToY := (*string)(ptrToY)
	*realPtrToY = v
}

func change_b_val(f *B, v []string) {
	pointerVal := reflect.ValueOf(f)
	val := reflect.Indirect(pointerVal)
	member := val.FieldByName("val")
	ptrToY := unsafe.Pointer(member.UnsafeAddr())
	realPtrToY := (*[]string)(ptrToY)
	*realPtrToY = v
}

func change_redis_val(f *redis.StringCmd, v string) {
	pointerVal := reflect.ValueOf(f)
	val := reflect.Indirect(pointerVal)
	member := val.FieldByName("val")
	ptrToY := unsafe.Pointer(member.UnsafeAddr())
	realPtrToY := (*[]byte)(ptrToY)
	*realPtrToY = []byte(v)
}

func change_redis_slice_val(f *redis.StringSliceCmd, v []string) {
	pointerVal := reflect.ValueOf(f)
	val := reflect.Indirect(pointerVal)
	member := val.FieldByName("val")
	ptrToY := unsafe.Pointer(member.UnsafeAddr())
	realPtrToY := (*[]string)(ptrToY)
	*realPtrToY = v
}

func main(){
	m := redis.NewStringCmd("KEYS", "driver*")
	change_redis_val(m, "victory")
	fmt.Println("Redis value:", m.Val())

	m2 := redis.NewStringSliceCmd("HMGET", "option")
	change_redis_slice_val(m2, []string{"1", "2", "3"})
	fmt.Println("Redis slice value:", m2.Val())

	a := new(A)
	change_val(a, "lalalal")
	fmt.Println(a.Val())

	b := new(B)
	change_b_val(b, []string{"1", "2", "3"})
	fmt.Println(b.Val())
}