// Created on savesnippets.com · https://savesnippets.com/72eZmrsGM4gVtf
package main

import (
    "encoding/json"
    "fmt"
)

type User struct {
    ID        int    `json:"id"`
    Username  string `json:"username"`
    Email     string `json:"email,omitempty"`        // skip if empty string
    Password  string `json:"-"`                       // never marshal
    CreatedAt string `json:"created_at"`
}

func main() {
    u := User{
        ID:        42,
        Username:  "alice",
        Email:     "",                                // will be omitted
        Password:  "hunter2",                         // never appears in JSON
        CreatedAt: "2025-03-12T14:00:00Z",
    }
    b, _ := json.MarshalIndent(u, "", "  ")
    fmt.Println(string(b))
    // {
    //   "id": 42,
    //   "username": "alice",
    //   "created_at": "2025-03-12T14:00:00Z"
    // }
}