Interface types

An interface type specifies a set of methods that a concrete type must possess to be considered an instance of that interface.

An interface type specifies a method set called its interface. A variable of interface type can store a value of any type with a method set that is any superset of the interface. Such a type is said to implement the interface. The value of an uninitialized variable of interface type is nil.

Here is a go lang example that shows how to use an interface.

Source: (example.go)

package main
 
import "fmt"
 
type Pet interface {
   speak()
}
 
func speak(p Pet) {
   p.speak()
}
 
type Cat struct {
   Pet
}
 
func (c Cat) speak() {
   fmt.Println("I am a cat.")
}
 
type Dog struct {
   Pet
}
 
func (d Dog) speak() {
   fmt.Println("I am a Dog.")
}
 
func main() {
 
   c := &Cat{}
   speak(c)
 
   d := &Dog{}
   speak(d)
 
}
 

Output:

$ go run example.go
I am a cat.
I am a Dog.