struct

// Define a struct
type StructName struct {
    FieldName Type
    FieldName Type
}

// Initialization
s1 := StructName{value1, value2}              // By field order (not recommended)
s2 := StructName{FieldName: value}            // By field name (recommended)
var s3 StructName                              // Initialized to zero values
s4 := new(StructName)                          // Returns *StructName

// Accessing a field
s2.FieldName

// Struct embedding (promotes fields and methods of another struct, similar to inheritance)
type Parent struct { ... }
type Child struct {
    Parent              // Embedded without a field name
    ExtraField Type
}

package main

import "fmt"

// A basic struct definition.
type Person struct {
    Name string
    Age  int
}

// An example of struct embedding.
type Address struct {
    City    string
    Country string
}

type Employee struct {
    Person          // Promotes Person's fields and methods.
    Address         // Promotes Address's fields.
    Department string
}

// Struct with JSON tags (used together with encoding/json)
type Product struct {
    ID    int    `json:"id"`
    Name  string `json:"name"`
    Price float64 `json:"price,omitempty"` // Omitted when the value is zero.
}

func main() {
    // Initialize a struct (using field names is recommended)
    p := Person{Name: "Taro Yamada", Age: 30}
    fmt.Printf("Name: %s, Age: %d\n", p.Name, p.Age)

    // Modify a field via a pointer.
    pp := &p
    pp.Age = 31 // Same as (*pp).Age = 31. Go dereferences automatically.
    fmt.Println("Age after birthday:", p.Age)

    fmt.Println()

    // Embedded structs
    emp := Employee{
        Person:     Person{Name: "Hanako Suzuki", Age: 25},
        Address:    Address{City: "Tokyo", Country: "Japan"},
        Department: "Engineering",
    }
    // Promoted fields can be accessed directly.
    fmt.Println("Name:", emp.Name)         // Same as emp.Person.Name
    fmt.Println("City:", emp.City)          // Same as emp.Address.City
    fmt.Println("Department:", emp.Department)

    fmt.Println()

    // Anonymous struct (for temporary use such as test data)
    point := struct {
        X, Y int
    }{X: 10, Y: 20}
    fmt.Printf("Coordinates: (%d, %d)\n", point.X, point.Y)
}

Structs are used in place of classes in Go. Whether a field is exported (visible outside the package) depends on whether its name starts with an uppercase letter — uppercase means exported, lowercase means unexported. Structs are value types, so assignment and function arguments copy the entire value. Use a pointer when passing large structs to functions for better performance.

If a struct field name starts with a lowercase letter, it is invisible outside its package and cannot be handled by packages such as encoding/json or reflect. Always start field names with an uppercase letter if they need to be exported.

For adding methods to structs, see Method / Receiver. For combining structs with interfaces, see interface.