Go
Challenge 4 - Mini app
Write an inventory with map, struct and function.
Challenge: a phone book
You will write a small phone book app combining maps, structs and functions. The Rehber type keeps people in a map by name and offers three methods:
type Kisi struct {
Ad string
Tel string
}
type Rehber struct{ kisiler map[string]Kisi }
func (r *Rehber) Ekle(k Kisi) error // error if the name already exists
func (r *Rehber) Bul(ad string) (Kisi, bool)
func (r *Rehber) Liste() []string // names, alphabetical
Plan
1) Ekle: if r.kisiler == nil, create it with make; check for duplicates with _, exists := r.kisiler[k.Ad] and return fmt.Errorf("%s zaten kayıtlı", k.Ad); otherwise add. 2) Bul: return with comma-ok. 3) Liste: collect the keys into a slice and sort them with slices.Sort.
Exercise Phone book app
Write Rehber following the plan. Add Can and Ada, try adding Ada again and print the error; then print r.Liste() and the phone number found with r.Bul("Can").
Show example solution
package main
import (
"fmt"
"slices"
)
type Kisi struct {
Ad string
Tel string
}
type Rehber struct{ kisiler map[string]Kisi }
func (r *Rehber) Ekle(k Kisi) error {
if r.kisiler == nil {
r.kisiler = make(map[string]Kisi)
}
if _, exists := r.kisiler[k.Ad]; exists {
return fmt.Errorf("%s zaten kayıtlı", k.Ad)
}
r.kisiler[k.Ad] = k
return nil
}
func (r *Rehber) Bul(ad string) (Kisi, bool) {
k, ok := r.kisiler[ad]
return k, ok
}
func (r *Rehber) Liste() []string {
adlar := make([]string, 0, len(r.kisiler))
for ad := range r.kisiler {
adlar = append(adlar, ad)
}
slices.Sort(adlar)
return adlar
}
func main() {
var r Rehber
r.Ekle(Kisi{"Can", "555-0101"})
r.Ekle(Kisi{"Ada", "555-0199"})
fmt.Println(r.Ekle(Kisi{"Ada", "555-0000"}))
fmt.Println(r.Liste())
if k, ok := r.Bul("Can"); ok {
fmt.Println(k.Tel)
}
}
Test yourself
-
Why can <code>var r Rehber; r.Ekle(...)</code> crash?
- It doesn't crash
- The kisiler map is nil and you can't write to a nil map
- Ekle is undefined
- Rehber must be a pointer
Show answer
The kisiler map is nil and you can't write to a nil map — Creating the map with make inside Ekle when it is nil (or writing a NewRehber constructor) prevents this error.
-
Initialize the map
if r.kisiler == nil {
r.kisiler = ____(map[string]Kisi)
}
Show answer
if r.kisiler == nil {
r.kisiler = make(map[string]Kisi)
}
-
Method and return
- Ekle
- error
- Bul
- (Kisi, bool)
- List
- []string (sorted)
- nil map
- Initialize with make
Next lesson: Beginner section exam
