CodeBlanks Logo Icon CodeBlanks
Login Register

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)

Practice 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.

Starter code

main.go
package main

import "fmt"

func main() {
    // buraya yaz
}

Sample solution

main.go
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)
}

Expected output

Ada - İzmir

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Why doesn't <code>Kitap{"Dune", 412}</code> (Yazar omitted) compile?

  • 412 isn't a string and goes to Yazar
  • Both are true Correct answer
  • It compiles
  • The positional form must give every field

Explanation: 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.

2 Named field

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

Explanation: In the named-field form, the field name is written before the colon.

3 Form and result

Term Meaning
Kitap{Title: "X"} Others zero
Kitap{"X", "Y", 1} Positional, all fields
&Kitap{} *Kitap
struct{ X int }{1} Anonymous struct

All lessons in Beginner

1 Go basics

  1. What is Go?
  2. Installing Go
  3. Your first program
  4. go run and go build
  5. Comments and semicolons
  6. Summary - Go basics

2 Modules

  1. go mod init
  2. package and import
  3. The main package
  4. Multiple files
  5. go.sum and dependencies
  6. Summary - Modules

3 Variables

  1. Declaration with var
  2. Short declaration :=
  3. const and iota
  4. Zero value
  5. Type inference
  6. Summary - Variables

4 Data types

  1. int and float
  2. bool and string
  3. byte and rune
  4. Type conversion
  5. Type definitions
  6. Summary - Data types

5 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Command-line menu

6 Functions

  1. func declaration
  2. Parameters and return
  3. Multiple return
  4. Variadic functions
  5. Anonymous functions
  6. Summary - Functions

7 Control flow

  1. if, else if, else
  2. for loop
  3. Iterating with range
  4. switch and fallthrough
  5. break and continue
  6. Summary - Control flow

8 Array and slice

  1. Array declaration
  2. Slice declaration
  3. Appending with append
  4. Sub-slice
  5. len and cap
  6. Summary - Array and slice

9 Project: Shopping cart

  1. Product struct
  2. Adding to cart
  3. Computing total
  4. Printing the cart

10 Map

  1. Map declaration
  2. Adding elements
  3. Looking up in a map
  4. Deleting from a map
  5. Iterating a map with range
  6. Summary - Map

11 String

  1. String and byte
  2. String concatenation
  3. Conversion with strconv
  4. The strings package
  5. Rune and UTF-8
  6. Summary - String

12 Pointer

  1. What is a pointer?
  2. & and * operators
  3. The new function
  4. Pointers and functions
  5. Nil pointer
  6. Summary - Pointer

13 Struct

  1. Struct declaration
  2. Creating a struct
  3. Field access
  4. Struct embedding
  5. Struct and pointer
  6. Summary - Struct

14 Methods

  1. Method declaration
  2. Pointer receiver
  3. Value receiver
  4. Methods and embedding
  5. Method chaining
  6. Summary - Methods

15 Interface and error

  1. Interface declaration
  2. Implicit satisfaction
  3. The error interface
  4. Returning errors
  5. errors.Is and errors.As
  6. Summary - Interface and error

16 Beginner final

  1. Challenge 1 - Combined program
  2. Challenge 2 - Data structure
  3. Challenge 3 - Error handling
  4. Challenge 4 - Mini app