Creating a struct

Learn to create struct values and assign fields.

Creating structs

A struct value is created in three ways:

k1 := Kitap{Title: "Dune", Sayfa: 412}  // named fields (recommended)
k2 := Kitap{"Dune", "Herbert", 412}       // positional, all fields
k3 := &Kitap{Title: "Dune"}              // a pointer

With named fields, omitted fields get their zero value (k1.Yazar == ""). The positional form must give every field and breaks when a field is added to the struct.

Anonymous and nested structs

An unnamed struct can be used for one-off data; it is common in tests and JSON responses:

nokta := struct{ X, Y int }{3, 4}
fmt.Println(nokta.X)  // 3

A struct field can be another struct:

type Adres struct{ Sehir string }
type Kisi struct {
    Ad    string
    Adres Adres
}
k := Kisi{Ad: "Ada", Adres: Adres{Sehir: "İzmir"}}
fmt.Println(k.Adres.Sehir)

Exercise Nested struct

Define the structs Adres (Sehir string) and Kisi (Ad string, Adres Adres). Create Kisi{Ad: "Ada", Adres: Adres{Sehir: "İzmir"}} with named fields and print k.Ad + " - " + k.Adres.Sehir.

Show example solution

package main

import "fmt"

type Adres struct{ Sehir string }

type Kisi struct {
    Ad    string
    Adres Adres
}

func main() {
    k := Kisi{Ad: "Ada", Adres: Adres{Sehir: "İzmir"}}
    fmt.Println(k.Ad + " - " + k.Adres.Sehir)
}

Test yourself

Why doesn't <code>Kitap{"Dune", 412}</code> (Yazar omitted) compile?
- 412 isn't a string and goes to Yazar
- Both are true
- It compiles
- The positional form must give every field
Show answer

Both are true — The positional form must match the field count; also 412 would be assigned to the second field, Yazar (a string). The named-field form avoids this mistake.

Named field

k := Kitap{____: "Dune", Sayfa: 412}

Show answer

k := Kitap{Title: "Dune", Sayfa: 412}

Form and result

Kitap{Title: "X"}

Others zero
Kitap{"X", "Y", 1}

Positional, all fields
&Kitap{}

*Kitap
struct{ X int }{1}

Anonymous struct

Next lesson: Field access

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