Reflection

reflect.TypeOf and reflect.ValueOf

Reflection lets you inspect and manipulate types at runtime. It's used by encoding/json, ORMs, and validation libraries. But it's slow and loses type safety — use sparingly.

import "reflect"

x := 42
t := reflect.TypeOf(x)
v := reflect.ValueOf(x)

fmt.Println("Type:", t)           // int
fmt.Println("Value:", v)          // 42
fmt.Println("Kind:", t.Kind())    // int

Struct Tags

type User struct {
    Name  string `json:"name" validate:"required"`
    Email string `json:"email" validate:"email"`
    Age   int    `json:"age,omitempty"`
}

t := reflect.TypeOf(User{})
for i := 0; i < t.NumField(); i++ {
    field := t.Field(i)
    fmt.Printf("%s: json=%s validate=%s\n",
        field.Name,
        field.Tag.Get("json"),
        field.Tag.Get("validate"))
}

Name: json=name validate=required
Email: json=email validate=email
Age: json=age,omitempty validate=

Practice Exercises