go语言学习五 - 接口和“多态”

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package main   import (     "errors"     "fmt" )   func main() {       if x, e := DOCFactory("XXX"); e == nil {         x.Summary()     } else {         fmt.Println(e.Error())     } }   type Article struct{ Topic string }   type News struct{ Title string }   type Doc interface{ Summary() }   func (a Article) Summary() {     fmt.Printf("Article topic is %s", a.Topic) }   func (n News) Summary() {     fmt.Printf("News title is %s", n.Title) }   func DOCFactory(t string) (Doc, error) {     switch t {     case "Article":         return Article{"aaa"}, nil     case "News":         return News{"bbb"}, nil     default:         return nil, errors.New("no such struct")     } }