golang中的pair

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

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()   }