Struct declaration
- Go course
- Beginner
- Lesson 69/90
- 4 min
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 falseStructs with slice or map fields can't be compared with ==.
Practice 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.
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample 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)
}Expected output
412 500
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 After <code>var k Kitap</code>, what is <code>k.Sayfa</code>?
- 0 Correct answer
- nil
- Undefined
- A compile error
Explanation: Every field of a struct starts with its own zero value: string "", int 0.
2 Struct type
type Nokta ____ {
X, Y int
}type Nokta struct {
X, Y int
}Explanation: type Name struct { ... } defines a new struct type.
3 Field and visibility
| Term | Meaning |
|---|---|
Title |
Exported |
sayfa |
Package-private |
var k Kitap |
Zero-valued fields |
b := a |
All fields are copied |