main.go

package main

import (
	"fmt"
	"reflect"
)

const (
	Male = iota + 1
	Female
	Unknown
)

type (
	User struct {
		Name   string
		Gender int
		Age    int
	}
)

func MakeSlice(v interface{}) reflect.Value {
	typ := reflect.TypeOf(v)
	sli := reflect.SliceOf(typ)
	slice := reflect.MakeSlice(sli, 0, 0)
	x := reflect.New(slice.Type())
	x.Elem().Set(slice)
	return x.Elem()
}

func main() {
	var x reflect.Value

	apply := func(x reflect.Value) {
		var v interface{}
		switch x.Interface().(type) {
		case []User:
			v = []User{
				{"kaneshin", Male, 27},
			}
		case []*User:
			v = []*User{
				{"gopher", Unknown, 6},
			}
		}
		x.Set(reflect.ValueOf(v))
	}

	output := func(x reflect.Value) {
		fmt.Printf("Type is %+T\n", x.Interface())
		for i := 0; i < x.Len(); i++ {
			fmt.Printf("- %+v\n", x.Index(i).Interface())
		}
		fmt.Println()
	}

	// Make []User
	x = MakeSlice(User{})
	apply(x)
	output(x)

	// Make []*User
	x = MakeSlice(new(User))
	apply(x)
	output(x)
}