setting a nil pointer to a slice in a struct using reflection - go

Question

I'm practicing reflections using go and I'm trying to achieve the following,
to have a struct type, with a field that is a pointer to a slice of strings.
now that pointer is nil, i want to create the slice, add a value and set that pointer in the struct to point to the newly created slice, and to do all of that using reflections.
I created the following sample code to demonstrate what I'm doing:
package main
import (
"log"
"reflect"
)
type UserInfo struct {
Name string
Roles *[]string
UserId int
}
func main() {
var myV UserInfo
myV.Name="moshe"
myV.UserId=5
v := reflect.ValueOf(&myV.Roles)
t := reflect.TypeOf(myV.Roles)
myP := reflect.MakeSlice(t.Elem(),1,1)
myP.Index(0).SetString("USER")
v.Elem().Set(reflect.ValueOf(&myP)) <-- PANIC HERE
log.Print(myV.Roles)
}
this panics the message
panic: reflect.Set: value of type *reflect.Value is not assignable to type *[]string
of course the slice does not create a pointer so if i do this:
v.Elem().Set(myP.Convert(v.Elem().Type()))
I get
panic: reflect.Value.Convert: value of type []string cannot be converted to type *[]string
but when I try to convert the address with
v.Elem().Set(reflect.ValueOf(&myP).Convert(v.Elem().Type()))
I get
panic: reflect.Value.Convert: value of type *reflect.Value cannot be converted to type *[]string
what am I still missing?
thanks!

Answer 1

You are attempting to set the value using a reflect.Value of a pointer to a reflect.Value, which is definitely not the same as a *[]string
Build the value up in steps and work your way outwards:
// create the []string, and set the element
slice := reflect.MakeSlice(t.Elem(), 1, 1)
slice.Index(0).SetString("USER")
// create the *[]string pointer, and set its value to point to the slice
ptr := reflect.New(slice.Type())
ptr.Elem().Set(slice)
// set the pointer in the struct
v.Elem().Set(ptr)
https://play.golang.org/p/Tj_XeXNNsML