where is the indication that we are implementing that interface?

Hi, Below is the example code which explains basic interfaces
 

package main



import "fmt"



type Guitarist interface {

    // PlayGuitar prints out "Playing Guitar"

    // to the terminal

    PlayGuitar()

}



type BaseGuitarist struct {

    Name string

}



type AcousticGuitarist struct {

    Name string

}



func (b BaseGuitarist) PlayGuitar() {

    fmt.Printf("%s plays the Bass Guitar\n", b.Name)

}



func (b AcousticGuitarist) PlayGuitar() {

    fmt.Printf("%s plays the Acoustic Guitar\n", b.Name)

}



func main() {

    var player BaseGuitarist

    player.Name = "Paul"

    player.PlayGuitar()



    var player2 AcousticGuitarist

    player2.Name = "Ringo"

    player2.PlayGuitar()

}

 
without this interface also, above program giving correct output,
 

type Guitarist interface {

    // PlayGuitar prints out "Playing Guitar"

    // to the terminal

    PlayGuitar()

}

 
then what use of interface here , and where is the indication that we are implementing that interface?