Go: struct を map に変換

// ----------------------------------------------------------------
//
//  struct_to_map.go
//
//                Jan/31/2021
//
// ----------------------------------------------------------------
package main

import (
    "fmt"
    "reflect"
)

type City struct {
    Id  string
    Name_city   string
    Population  int
    Date_mod    string
}

// ---------------------------------------------------------------
func main() {
    fmt.Println ("*** 開始 ***")

    aa := City{Id: "t0921", Name_city: "宇都宮", Population: 34126, Date_mod: "2018-3-2"}

    fmt.Println (aa)

    unit_aa := make (map[string]interface{})

    tt := reflect.TypeOf(aa)
    vv := reflect.ValueOf(aa)

    for it:=0; it < tt.NumField(); it++ {
        ff := tt.Field(it)
        key := ff.Name
        value := vv.FieldByName(key).Interface()

        fmt.Println(key, value)

        unit_aa[key] = value
        }

    fmt.Println (unit_aa)

    fmt.Println ("*** 終了 ***")
}

// ----------------------------------------------------------------

$ go run struct_to_map.go
*** 開始 ***
{t0921 宇都宮 34126 2018-3-2}
Id t0921
Name_city 宇都宮
Population 34126
Date_mod 2018-3-2
map[Date_mod:2018-3-2 Id:t0921 Name_city:宇都宮 Population:34126]
*** 終了 ***