Struct Teglari

Struct tegi (tag) — maydonga biriktirib qo’yiladigan, matn ko’rinishidagi metama’lumot; teskari qo’shtirnoq (backtick) ichida yoziladi. Go’ning o’zi bu teglarni ishlatmaydi — ular boshqa paketlar uchun ko’rsatma, xolos. Eng ko’p uchraydigan joyi — encoding/json: teg JSON kalitini belgilaydi (omitempty bo’sh maydonni tashlab ketadi, - esa maydonni butunlay chiqarib tashlaydi).

json-tags.go


package main
 
import (
    "encoding/json"
    "fmt"
)
 
type Account struct {
    Username string `json:"username"`
    Bio      string `json:"bio,omitempty"`
    Password string `json:"-"`
}
 
func main() {
    a := Account{Username: "gopher", Bio: "", Password: "maxfiy123"}
    data, _ := json.Marshal(a)
    fmt.Println(string(data))
}


$ go run json-tags.go
{"username":"gopher"}

Xulosa: teg tufayli kalit username bo’lib chiqdi, Bio bo’sh edi — omitempty uni tashlab yubordi, Password esa - tufayli hech qachon ko’rinmaydi.

Teglar oddiy matn, shuning uchun ularni reflect orqali o’zingiz ham o’qiy olasiz — encoding/json ham xuddi shunday qiladi:

reflect-tags.go


package main
 
import (
    "fmt"
    "reflect"
)
 
type Product struct {
    Name  string `json:"name" validate:"required"`
    Price int    `json:"price" validate:"min=0"`
}
 
func main() {
    t := reflect.TypeOf(Product{})
    for i := 0; i < t.NumField(); i++ {
        f := t.Field(i)
        fmt.Printf("%s -> json=%q, validate=%q\n", f.Name, f.Tag.Get("json"), f.Tag.Get("validate"))
    }
}


$ go run reflect-tags.go
Name -> json="name", validate="required"
Price -> json="price", validate="min=0"

Xulosa: Tag.Get("kalit") bilan istalgan tegni o’qiy olasiz — validatsiya, ORM (Object-Relational Mapping) va JSON kutubxonalarining hammasi shu mexanizm ustiga qurilgan.

Manba / batafsil: encoding/json.Marshal , reflect.StructTag