Demo=> Interface in Go

demo_http_request.go

package main

import (
	"fmt"
	"net/http"
)

type Counter struct {
	n int
}

func (ctr *Counter) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	ctr.n++
	fmt.Fprintf(w, "counter = %d\n", ctr.n)
}

func main() {
	ctr := new(Counter)
	http.Handle("/counter", ctr)
	http.ListenAndServe("localhost:8888", nil)
}

demo_shape.go

package main

import "fmt"

type Shaper interface {
	Area() float64
}

type Rectangle struct {
	width  float64
	height float64
}

func (rectangle Rectangle) Area() float64 {
	return rectangle.width * rectangle.height
}

type Square struct {
	width float64
}

func (square Square) Area() float64 {
	return square.width * square.width
}

type Circle struct {
	redius float64
}

func (circle Circle) Area() float64 {
	return circle.redius * circle.redius * 3.1415
}

func ComputeArea(shape Shaper) {
	fmt.Printf("Area of %+v=%.3f\n", shape, shape.Area())
}

func main() {
	rectangle := Rectangle{5, 10}
	square := Square{5}
	circle := Circle{5}

	shapes := [...]Shaper{rectangle, square, circle}
	for _, shape := range shapes {
		ComputeArea(shape)
	}

}