package main

import "fmt"

type Reader interface {

	ReadBook()

}

type Writer interface {

	WriteBook()

}

// 具体类型

type Book struct {}

func (b *Book) ReadBook() {

	fmt.Println("Read a Book")

}

func (b *Book) WriteBook() {

	fmt.Println("Write a Book")

}

func main() {

	// b: pair<type:Book, value:book{}地址>

	b := &Book{}

	// r: pair<type:, value:>

	var r Reader

	// r: pair<type:Book, value:book{}地址>

	r = b

	r.ReadBook()

	// w: pair<type:, value:>

	var w Writer

	// w: pair<type:Book, value:book{}地址>

	// 此处的断言为什么会成功？因为w r 具体的type是一致的，所以会断言成功

	w = r.(Writer)

	w.WriteBook()

}