Interface declaration

Context

An interface defines a set of method signatures. In Go, interfaces are satisfied implicitly – a type implements an interface if it provides all the methods declared in the interface. No explicit implements keyword is needed.

Example

Define an interface Speaker and two structs that implement it.

Code example

package main

import "fmt"

type Speaker interface {
    Speak() string
}

type Dog struct{}
func (d Dog) Speak() string { return "Woof!" }

type Cat struct{}
func (c Cat) Speak() string { return "Meow!" }

func makeSound(s Speaker) {
    fmt.Println(s.Speak())
}

func main() {
    dog := Dog{}
    cat := Cat{}
    makeSound(dog)
    makeSound(cat)
}

Output

Woof!
Meow!

Useful links

• Go spec: Interface types
• Go by Example: Interfaces