Go
Methods and embedding
Learn how embedded struct methods are promoted.
Methods and embedding
The methods of an embedded struct are also promoted to the outer struct; the outer type calls them as if they were its own:
type Kayitci struct{ Onek string }
func (k Kayitci) Logla(m string) { fmt.Println(k.Onek + m) }
type Servis struct {
Kayitci
Ad string
}
s := Servis{Kayitci{"[api] "}, "sepet"}
s.Logla("başladı") // [api] başladı
This way shared behavior is reused without inheritance.
Shadowing and wrapping
The outer type can extend behavior by defining a method with the same name and calling the embedded one from inside:
func (s Servis) Logla(m string) {
s.Kayitci.Logla(s.Ad + ": " + m)
}
s.Logla("başladı") // [api] sepet: başladı
This pattern is Go's counterpart to "calling the superclass method" in other languages, but explicit and visible.
Exercise Wrapped logger
Write the Kayitci type above and Servis, which embeds it; Servis's own Logla method prepends s.Ad + ": " to the message and calls the embedded Logla. Run Servis{Kayitci{"[api] "}, "sepet"}.Logla("başladı").
Show example solution
package main
import "fmt"
type Kayitci struct{ Onek string }
func (k Kayitci) Logla(m string) { fmt.Println(k.Onek + m) }
type Servis struct {
Kayitci
Ad string
}
func (s Servis) Logla(m string) {
s.Kayitci.Logla(s.Ad + ": " + m)
}
func main() {
Servis{Kayitci{"[api] "}, "sepet"}.Logla("başladı")
}
Test yourself
-
If Servis defines its own <code>Logla</code> method, which does <code>s.Logla("x")</code> call?
- Both
- A compile error
- Servis's own Logla
- Kayitci's Logla
Show answer
Servis's own Logla — The outer type's method shadows the embedded one; the embedded method can still be called with s.Kayitci.Logla("x").
-
Call the embedded method
func (s Servis) Logla(m string) {
s.____.Logla(s.Ad + ": " + m)
}
Show answer
func (s Servis) Logla(m string) {
s.Kayitci.Logla(s.Ad + ": " + m)
}
-
Call and result
- s.Logla (Servis'te yoksa)
- Kayitci.Logla
- s.Logla (Servis'te varsa)
- Servis.Logla
- s.Kayitci.Logla
- Always the embedded one
- Embedding
- Reuse
Next lesson: Method chaining
