Struct declaration

Learn to define a struct with type.

Defining structs

A struct is a type that groups related data into named fields:

type Kitap struct {
    Title string
    Yazar  string
    Sayfa  int
}

Fields starting with an upper-case letter are visible outside the package (and to libraries such as JSON); lower-case ones only inside it. Go has no classes; data is expressed with structs and behavior with methods.

Comparing structs

Structs whose fields are all comparable can be compared with == and can be map keys. When a struct is assigned, all of its fields are copied:

a := Kitap{"Dune", "Herbert", 412}
b := a
b.Sayfa = 500
fmt.Println(a.Sayfa, a == b)  // 412 false

Structs with slice or map fields can't be compared with ==.

Exercise Book struct

Define the Kitap struct (Title, Yazar, Sayfa). Create a := Kitap{"Dune", "Herbert", 412}, copy it with b := a, set b.Sayfa = 500 and print a.Sayfa and b.Sayfa.

Show example solution

package main

import "fmt"

type Kitap struct {
    Title string
    Yazar  string
    Sayfa  int
}

func main() {
    a := Kitap{"Dune", "Herbert", 412}
    b := a
    b.Sayfa = 500
    fmt.Println(a.Sayfa, b.Sayfa)
}

Test yourself

After <code>var k Kitap</code>, what is <code>k.Sayfa</code>?
- 0
- nil
- Undefined
- A compile error
Show answer

0 — Every field of a struct starts with its own zero value: string "", int 0.

Struct type

type Nokta ____ {
    X, Y int
}

Show answer

type Nokta struct {
    X, Y int
}

Field and visibility

Title

Exported
sayfa

Package-private
var k Kitap

Zero-valued fields
b := a

All fields are copied

Next lesson: Creating a struct

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