Interface object transformation in Go language

    There are two ways to transform interface objects in Go.

method one

• instance, ok := access object. (actual type)
• If the interface object is the corresponding actual type, then instance is the object after transformation, and the value of ok is true
• Use with if… else if… statement

Way two

• Connection object. (type)
• Use with switch...case statement

    The case is as follows:
//myInterfaceChg.go

// myInterfaceChg project main.go
package main

import (
	"fmt"
	"math"
)

//1.定义一个接口
type Shape interface {
	perimeter() float64
	area() float64
}

//2.矩形
type Rectangle struct {
	a, b float64
}

//3.三角形
type Triangle struct {
	a, b, c float64
}

//圆形
type Circle struct {
	radius float64
}

//实现接口的方法
func (r Rectangle) perimeter() float64 {
	return 2 * (r.a + r.b)
}

func (r Rectangle) area() float64 {
	return r.a * r.b
}

func (t Triangle) perimeter() float64 {
	return t.a + t.b + t.c
}

func (t Triangle) area() float64 {
	p := t.perimeter() / 2 //半周长
	//海伦公式
	s := math.Sqrt(p * (p - t.a) * (p - t.b) * (p - t.c))
	return s
}

func (c Circle) perimeter() float64 {
	return 2 * math.Pi * c.radius
}

func (c Circle) area() float64 {
	return math.Pow(c.radius, 2) * math.Pi
}

//测试函数
func testShape(s Shape) {
	fmt.Printf("  周长: %.2f, 面积: %.2f\n", s.perimeter(), s.area())
}

//接口对象转型--方式1
func getType(s Shape) {
	if instance, ok := s.(Rectangle); ok {
		fmt.Printf("该图是矩形, 长度为%.2f, 宽为%.2f, \t\n", instance.a, instance.b)
	} else if instance, ok := s.(Triangle); ok {
		fmt.Printf("该图是三角形, 三边分别为%.2f, %.2f, %.2f, \t\n", instance.a, instance.b, instance.c)
	} else if instance, ok := s.(Circle); ok {
		fmt.Printf("该图是圆形, 半径为%.2f, \t\n", instance.radius)
	}
}

//接口对象转型--方式2
func getTyep2(s Shape) {
	switch instance := s.(type) {
	case Rectangle:
		fmt.Printf("该图是矩形, 长度为%.2f, 宽为%.2f, \t\n", instance.a, instance.b)
	case Triangle:
		fmt.Printf("该图是三角形, 三边分别为%.2f, %.2f, %.2f, \t\n", instance.a, instance.b, instance.c)
	case Circle:
		fmt.Printf("该图是圆形, 半径为%.2f, \t\n", instance.radius)
	}
}

func main() {
	//fmt.Println("Hello World!")
	var s Shape
	s = Rectangle{3, 4}
	getType(s)
	testShape(s)

	s = Triangle{3, 4, 5}
	getType(s)
	testShape(s)

	s = Circle{1}
	getType(s)
	testShape(s)
}

    The effect is as follows:

Figure (1) Interface object transformation