Adding to cart
- Go course
- Beginner
- Lesson 48/90
- 6 min
Add products to the cart with append.
Adding to the cart
The cart is a slice of products. Adding is done with append. If the same product is added a second time, its quantity should increase instead of adding a new row; so the cart is searched first:
type Sepet struct{ Urunler []Urun }
func (s *Sepet) Ekle(u Urun) {
for i := range s.Urunler {
if s.Urunler[i].Ad == u.Ad {
s.Urunler[i].Adet += u.Adet
return
}
}
s.Urunler = append(s.Urunler, u)
}Changing with for i := range
Using for _, u := range s.Urunler while increasing the quantity doesn't work: u is a copy and the change doesn't reach the slice. That's why we iterate by index and change it through s.Urunler[i].Adet. This is one of the most common mistakes for Go beginners.
Practice The Ekle method
Write Urun, Sepet and the Ekle method. Add Kalem (3), Defter (1) and Kalem again (2) to the cart. Print the number of products and the pen's quantity.
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample solution
package main
import "fmt"
type Urun struct {
Ad string
Fiyat float64
Adet int
}
type Sepet struct{ Urunler []Urun }
func (s *Sepet) Ekle(u Urun) {
for i := range s.Urunler {
if s.Urunler[i].Ad == u.Ad {
s.Urunler[i].Adet += u.Adet
return
}
}
s.Urunler = append(s.Urunler, u)
}
func main() {
var s Sepet
s.Ekle(Urun{"Kalem", 12.5, 3})
s.Ekle(Urun{"Defter", 20, 1})
s.Ekle(Urun{"Kalem", 12.5, 2})
fmt.Println(len(s.Urunler), s.Urunler[0].Adet)
}Expected output
2 5
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Why does <code>Ekle</code> use a pointer receiver (<code>*Sepet</code>)?
- Because it is shorter
- Because slices require pointers
- It isn't required
- To change the cart itself; a value receiver would work on a copy Correct answer
Explanation: append returns a new slice header; writing it back to the Sepet permanently requires a pointer receiver.
2 Append to the end
s.Urunler = ____(s.Urunler, u)s.Urunler = append(s.Urunler, u)Explanation: append adds the new product to the end of the slice; the result is assigned back to the field.
3 Case and behavior
| Term | Meaning |
|---|---|
New product |
Added with append |
Existing product |
Quantity increases |
for _, u := range |
A copy, doesn't work |
*Sepet |
Lasting change |