GO结构体成员Tag中omitempty用法

如下所示结构体：

type Movie struct {
    Title  string
    Year   int  `json:"released"`
    Color  bool `json:"color,omitempty"`
    Actors []string
}

Color成员的Tag带了一个额外的omitempty选项，表示当Go语言结构体成员为空或零值时不生成该JSON对象。

package main

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

type Movie struct {
	Title  string
	Year   int  `json:"released"`
	Color  bool `json:"color,omitempty"`
	Actors []string
}

func main() {
	var movies = []Movie{
		{Title: "Casablanca", Year: 1942, Color: false,
			Actors: []string{"Humphrey Bogart", "Ingrid Bergman"}},
		{Title: "Cool Hand Luke", Year: 1967, Color: true,
			Actors: []string{"Paul Newman"}},
		{Title: "Bullitt", Year: 1968, Color: true,
			Actors: []string{"Steve McQueen", "Jacqueline Bisset"}},
	}

	data, err := json.MarshalIndent(movies, "", "  ")
	if err != nil {
		log.Fatalf("Failed to marshal JSON. error: %v", err)
		return
	}
	fmt.Printf("%s\n", data)

输出结果如下所示：

[
  {
    "Title": "Casablanca",
    "released": 1942,
    "Actors": [
      "Humphrey Bogart",
      "Ingrid Bergman"
    ]
  },
  {
    "Title": "Cool Hand Luke",
    "released": 1967,
    "color": true,
    "Actors": [
      "Paul Newman"
    ]
  },
  {
    "Title": "Bullitt",
    "released": 1968,
    "color": true,
    "Actors": [
      "Steve McQueen",
      "Jacqueline Bisset"
    ]
  }
]

从上面结果可以看出，Casablanca对应的对象中已经没有color属性了，因为false为bool类型的零值。