How to create a reflect slice

reflect_slice.go

package main

import (
	"fmt"
	"log"
	"reflect"
)

type S struct {
	N   int
	Str string
}

func testMap() {
	m := map[reflect.Value]bool{}

	s := &S{5, "foo"}
	s2 := &S{5, "foo"}
	rv1 := reflect.ValueOf(s)
	rv12 := reflect.ValueOf(s)
	rv2 := reflect.ValueOf(s2)
	fmt.Printf("rv1 == rv12: %v\n", rv1 == rv12)
	fmt.Printf("rv1 == rv2: %v\n", rv1 == rv2)
	m[rv1] = true
	fmt.Printf("m[rv1]:  %v\n", m[rv1])
	fmt.Printf("m[rv12]: %v\n", m[rv12])
	fmt.Printf("m[rv2]:  %v\n", m[rv2])
}

func fillStruct(results interface{}) error {
	rv := reflect.ValueOf(results)

	if rv.Type().Kind() != reflect.Ptr {
		return fmt.Errorf("results should be a pointer to a slice of pointers to struct, is %s. tp: %s", rv.Type().String(), rv.Type().String())
	}
	sliceV := rv.Elem()
	if sliceV.Type().Kind() != reflect.Slice {
		return fmt.Errorf("results should be a pointer to a slice of pointers to struct, is %s. sliceV.Type(): %s", rv.Type().String(), sliceV.Type().String())
	}

	// slice element should be a pointer to a struct
	sliceElemPtrType := sliceV.Type().Elem()
	if sliceElemPtrType.Kind() != reflect.Ptr {
		return fmt.Errorf("results should be a pointer to a slice of pointers to struct, is %s. sliceElemPtrType: %s", rv.Type().String(), sliceElemPtrType.String())
	}

	sliceElemType := sliceElemPtrType.Elem()
	if sliceElemType.Kind() != reflect.Struct {
		return fmt.Errorf("results should be a pointer to a slice of pointers to struct, is %s. sliceElemType: %s", rv.Type().String(), sliceElemType.String())
	}
	fmt.Printf("tp: %s, is nil: %v\n", rv.Type().String(), sliceV.IsNil())
	// if this is a pointer to nil slice
	if sliceV.IsNil() {
		sliceV.Set(reflect.MakeSlice(sliceV.Type(), 0, 0))
	}

	v := reflect.New(sliceElemType)
	sliceV2 := reflect.Append(sliceV, v)
	v = reflect.New(sliceElemType)
	sliceV2 = reflect.Append(sliceV2, v)
	sliceV.Set(sliceV2)
	return nil
}

func testFillStruct1() {
	var a []*S
	err := fillStruct(&a)
	if err != nil {
		log.Fatalf("fillStruct() failed with %s\n", err)
	}
	fmt.Printf("a: %v\nlen(a): %d\n", a, len(a))
}

func testFillStruct2() {
	var a = []*S{}
	err := fillStruct(&a)
	if err != nil {
		log.Fatalf("fillStruct() failed with %s\n", err)
	}
	fmt.Printf("a: %v\nlen(a): %d\n", a, len(a))
}

func main() {
	//testFillStruct1()
	//testFillStruct2()
	testMap()
}