Go设计模式之访问者模式讲解和代码示例

type visitor interface {
    visitForSquare(square)
    visitForCircle(circle)
    visitForTriangle(triangle)
}

func accept(v visitor)

func (obj *square) accept(v visitor){
    v.visitForSquare(obj)
}

package main
// 形状结构体
type Shape interface {
	getType() string
	accept(Visitor)
}

package main
type Square struct {
	side int
}
func (s *Square) accept(v Visitor) {
	v.visitForSquare(s)
}
func (s *Square) getType() string {
	return "Square"
}

package main
type Circle struct {
	radius int
}
func (c *Circle) accept(v Visitor) {
	v.visitForCircle(c)
}
func (c *Circle) getType() string {
	return "Circle"
}

package main
type Rectangle struct {
	l int
	b int
}
func (t *Rectangle) accept(v Visitor) {
	v.visitForrectangle(t)
}
func (t *Rectangle) getType() string {
	return "rectangle"
}

package main
type Visitor interface {
	visitForSquare(*Square)
	visitForCircle(*Circle)
	visitForrectangle(*Rectangle)
}

package main
import "fmt"
type AreaCalculator struct {
	area int
}
func (a *AreaCalculator) visitForSquare(s *Square) {
	fmt.Println("calculating area for square")
}
func (a *AreaCalculator) visitForCircle(s *Circle) {
	fmt.Println("Calculating area for circle")
}
func (a *AreaCalculator) visitForrectangle(s *Rectangle) {
	fmt.Println("Calculating area for rectangle")
}

package main
import "fmt"
type MiddleCoordinates struct {
	x int
	y int
}
func (a *MiddleCoordinates) visitForSquare(s *Square) {
	fmt.Println("Calculating middle point coordinates for square")
}
func (a *MiddleCoordinates) visitForCircle(c *Circle) {
	fmt.Println("Calculating middle point coordinates for circle")
}
func (a *MiddleCoordinates) visitForrectangle(t *Rectangle) {
	fmt.Println("Calculating middle point coordinates for rectangle")
}

package main
import "fmt"
func main() {
	square := &Square{side: 2}
	circle := &Circle{radius: 3}
	rectangle := &Rectangle{l: 2, b: 3}
	areaCalculator := &AreaCalculator{}
	square.accept(areaCalculator)
	circle.accept(areaCalculator)
	rectangle.accept(areaCalculator)
	fmt.Println()
	middleCoordinates := &MiddleCoordinates{}
	square.accept(middleCoordinates)
	circle.accept(middleCoordinates)
	rectangle.accept(middleCoordinates)
}