Summary - Struct

Combine struct, embedding and pointer to write a person record.

Structs summary

Structs are Go's data model: defined with type Name struct { ... }, created with named fields, copied on assignment, and supporting == when their fields are comparable. They are shared and changed through pointers (&T{}, p.Field). Embedding promotes the fields of other structs; tags give information to libraries.

Working on a slice of structs

In real programs structs are mostly kept in slices and filtered:

var uzun []Kitap
for _, k := range kitaplar {
    if k.Sayfa > 300 {
        uzun = append(uzun, k)
    }
}

slices.SortFunc(kitaplar, func(a, b Kitap) int { return a.Sayfa - b.Sayfa }) sorts a struct slice by a field.

Exercise Sorted books

Create a Kitap (Title string, Sayfa int) slice with {"Dune", 412}, {"Simyacı", 184}, {"Vakıf", 255}. Sort it by pages ascending with slices.SortFunc and print the titles in order on one line.

Show example solution

package main

import (
    "fmt"
    "slices"
)

type Kitap struct {
    Title string
    Sayfa  int
}

func main() {
    kitaplar := []Kitap{{"Dune", 412}, {"Simyacı", 184}, {"Vakıf", 255}}
    slices.SortFunc(kitaplar, func(a, b Kitap) int { return a.Sayfa - b.Sayfa })
    for _, k := range kitaplar {
        fmt.Print(k.Title, " ")
    }
    fmt.Println()
}

Test yourself

What do you see when printing a struct with <code>fmt.Printf("%+v", k)</code>?
- Only the values
- A memory address
- JSON
- Values with field names: {Title:Dune Sayfa:412}
Show answer

Values with field names: {Title:Dune Sayfa:412} — %v shows only the values, %+v also the field names, and %#v the Go syntax.

Print with fields

fmt.Printf("____
", Kitap{"Dune", 412})  // {Title:Dune Sayfa:412}

Show answer

fmt.Printf("%+v
", Kitap{"Dune", 412})  // {Title:Dune Sayfa:412}

Group summary

type T struct

Definition
T{Alan: x}

Named creation
Embedding

Composition
p.Alan

Automatic dereference

Next lesson: Method declaration

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