1. 变量的结构

2 举个例子

package mainimport "fmt"type Reader interface {ReadBook()
}type Writer interface {WriteBook()
}//具体类型
type Book struct {}func (this *Book) ReadBook() {fmt.Println("Read a Book")}func (this *Book) WriteBook() {fmt.Println("Write a Book")}func main() {//b: pair<type:Book,value:book>b := &Book{}//r: pair<type:,value>var r Reader//r:pair<type:Book,value:book{}地址>r = br.ReadBook()var w Writer//r：pair<type:Book,value:book()地址>w=r.(Writer)  //此处w r具体的type是一致的w.WriteBook()}