Go - 状態と振る舞い - 構造体 - JSONにエンコード、encodingインポートパス、jsonパッケージ、Marshal関数、MarshalIndent関数、構造体タグ

入門Goプログラミング
原著: Get Programming with Go
楽天ブックス Yahoo!

開発環境

• macOS Catalina - Apple (OS)
• Emacs (Text Editor)
• Windows 10 Pro (OS)
• Visual Studio Code (Text Editor)
• Go (プログラミング言語)

入門Goプログラミング (Nathan Youngman(著)、Roger Peppé(著)、吉川 邦夫(監修, 翻訳)、翔泳社)のUNIT 5(状態と振る舞い)、LESSON 21(構造体)の練習問題の解答を求めてみる。

コード

package main

import (
 "encoding/json"
 "fmt"
 "os"
)

type location struct {
 Name string  `json:"name"`
 Lat  float64 `json:"latitude"`
 Long float64 `json:"longitude"`
}

func exitOnError(err error) {
 if err != nil {
  fmt.Fprintf(os.Stderr, "%v\n", err)
  os.Exit(1)
 }
}
func main() {
 locations := []location{
  {Name: "Bradbury Landing", Lat: -4.5895, Long: 137.4417},
  {Name: "Columbia Memorial Station", Lat: -14.5684, Long: 175.472636},
  {Name: "Challenger Memorial Station", Lat: -19.462, Long: 354.4734},
 }
 bytes, err := json.Marshal(locations)
 exitOnError(err)
 fmt.Println(string(bytes))
 prefixes := []string{"", ">"}
 for _, prefix := range prefixes {
  fmt.Println("prefix", prefix)
  bytes, err = json.MarshalIndent(locations, prefix, "   ")
  exitOnError(err)
  fmt.Println(string(bytes))
 }
}

入出力結果(Zsh、PowerShell、Terminal)

% go run ./landing.go
[{"name":"Bradbury Landing","latitude":-4.5895,"longitude":137.4417},{"name":"Columbia Memorial Station","latitude":-14.5684,"longitude":175.472636},{"name":"Challenger Memorial Station","latitude":-19.462,"longitude":354.4734}]
prefix 
[
   {
      "name": "Bradbury Landing",
      "latitude": -4.5895,
      "longitude": 137.4417
   },
   {
      "name": "Columbia Memorial Station",
      "latitude": -14.5684,
      "longitude": 175.472636
   },
   {
      "name": "Challenger Memorial Station",
      "latitude": -19.462,
      "longitude": 354.4734
   }
]
prefix >
[
>   {
>      "name": "Bradbury Landing",
>      "latitude": -4.5895,
>      "longitude": 137.4417
>   },
>   {
>      "name": "Columbia Memorial Station",
>      "latitude": -14.5684,
>      "longitude": 175.472636
>   },
>   {
>      "name": "Challenger Memorial Station",
>      "latitude": -19.462,
>      "longitude": 354.4734
>   }
>]
%