Implicit satisfaction
- Go course
- Beginner
- Lesson 82/90
- 4 min
Learn that Go interfaces are satisfied implicitly.
Implicit satisfaction
In Go a type satisfies an interface implicitly: there is no implements keyword. If it has the required methods, the type is that interface:
type Ordek struct{}
func (Ordek) Ses() string { return "vak" }
type Robot struct{}
func (Robot) Ses() string { return "bip" }
for _, s := range []Sesli{Ordek{}, Robot{}} {
fmt.Println(s.Ses())
}This is called "duck typing", but in Go it is checked at compile time.
Compile-time check
To guarantee that a type satisfies an interface, an empty assignment is written; if a method is missing, compilation fails:
var _ Sesli = Ordek{} // Ordek must satisfy Sesli
var _ Sesli = (*Robot)(nil) // for pointer-receiver methodsIf a method is defined with a pointer receiver, only *T satisfies the interface; a T value doesn't.
Practice Sound-making types
Write the Sesli interface (Ses() string) and the types Ordek ("vak") and Robot ("bip"). Add var _ Sesli = Ordek{} as a compile-time check and print both types' sounds in order.
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample solution
package main
import "fmt"
type Sesli interface{ Ses() string }
type Ordek struct{}
type Robot struct{}
func (Ordek) Ses() string { return "vak" }
func (Robot) Ses() string { return "bip" }
var _ Sesli = Ordek{}
func main() {
for _, s := range []Sesli{Ordek{}, Robot{}} {
fmt.Println(s.Ses())
}
}Expected output
vak bip
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is the biggest advantage of implicit satisfaction?
- It runs faster
- No methods need to be written
- Mistakes are impossible
- Another package's type can satisfy your interface without that package changing Correct answer
Explanation: The consuming side defines the interface; standard types such as os.File satisfy it without their authors knowing about it.
2 Satisfaction check
var ____ Sesli = Ordek{}var _ Sesli = Ordek{}Explanation: Assigning to the blank identifier only performs a compile-time type check.
3 Concept
| Term | Meaning |
|---|---|
implements |
Not in Go |
Implicit satisfaction |
Methods are enough |
var _ I = T{} |
Compile-time check |
*T receiver |
Only *T satisfies |