package main

import "fmt"

type Dog struct {
    Name string
}

type Animal interface {
    Dog
    Speak()
}

func (d Dog) Speak() {
    fmt.Println("Woof!")
}

func main() {
    d := Dog{Name: "Fido"}
    fmt.Println(d)
    d.Speak()
}

Why does this code block not raise error?

Is this valid? If yes, then what are the use cases for it?