the-way-to-go_ZH_CN/eBook/examples/chapter_11/multi_interfaces_poly.go

//multi_interfaces_poly.go
package main

import "fmt"

type Shaper interface {
	Area() float32
}

type TopologicalGenus interface {
	Rank() int
}

type Square struct {
	side float32
}

func (sq *Square) Area() float32 {
	return sq.side * sq.side
}

func (sq *Square) Rank() int {
	return 1
}

type Rectangle struct {
	length, width float32
}

func (r Rectangle) Area() float32 {
	return r.length * r.width
}

func (r Rectangle) Rank() int {
	return 2
}

func main() {
	r := Rectangle{5, 3} // Area() of Rectangle needs a value
	q := &Square{5}      // Area() of Square needs a pointer
	shapes := []Shaper{r, q}
	fmt.Println("Looping through shapes for area ...")
	for n := range shapes {
		fmt.Println("Shape details: ", shapes[n])
		fmt.Println("Area of this shape is: ", shapes[n].Area())
	}
	topgen := []TopologicalGenus{r, q}
	fmt.Println("Looping through topgen for rank ...")
	for n := range topgen {
		fmt.Println("Shape details: ", topgen[n])
		fmt.Println("Topological Genus of this shape is: ", topgen[n].Rank())
	}
}

/* Output:
Looping through shapes for area ...
Shape details:  {5 3}
Area of this shape is:  15
Shape details:  &{5}
Area of this shape is:  25
Looping through topgen for rank ...
Shape details:  {5 3}
Topological Genus of this shape is:  2
Shape details:  &{5}
Topological Genus of this shape is:  1
*/