golang中的pair

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()

}