Go 接口 示例

package main

import (
	"fmt"
	"math"
)

type ShapeDesc interface {
	Area() float64
	Perimeter() float64
}

type rectangle struct {
	H, W float64
}

type circle struct {
	R float64
}

func (r rectangle) Area() float64 {
	return r.H * r.W
}

func (r rectangle) Perimeter() float64 {
	return 2 * (r.H + r.W)
}

func (c circle) Area() float64 {
	return c.R * c.R * math.Pi
}

func (c circle) Perimeter() float64 {
	return 2 * c.R * math.Pi
}

func Desc(s ShapeDesc) {
    // 类型断言
	_, ok := s.(circle)
	if ok {
		fmt.Println("This is circle.")
	}

	_, ok = s.(rectangle)
	if ok {
		fmt.Println("This is rectangle.")
	}

	fmt.Println("area:", s.Area())
	fmt.Println("perimeter:", s.Perimeter())
}

func main() {
	var s1, s2 ShapeDesc
	s1 = rectangle{H: 2, W: 3}
	s2 = circle{R: 2}
	Desc(s1)
	Desc(s2)
}