Thank you V. I'v read this before, but it doesn't answer my question. Thank you anyway!
在 2017年5月5日星期五 UTC+8下午7:46:42，Volker Dobler写道： > > See https://golang.org/doc/faq#convert_slice_of_interface > > V. > > On Friday, 5 May 2017 13:35:42 UTC+2, eZio Pan wrote: >> >> Hi, I'm a newbie in Golang. I get stuck in a problem that I can't >> understand why. I wish someone could help me out. Thanks! >> >> There are 2 struct type *S1* and *S2*. Both of them implement interface >> type *StringI*. >> I write a function called *run* which use *StringI* interface as input, >> and run all method *StringI* signatured. >> >> Then I write a test file, in which I declare a **S1* variable as *s1*, >> and a **S2* variable as *s2*. >> I create a slice *[]interface{}{s1,s2}*, the I use for loop to get item >> in it. >> >> But when I use *run*(*LoopedItem*), I got an error >> >> *cannot use item (type interface {}) as type StringI in argument to run* >> >> And I use fmt.Printf("%T", *LoopedItem*), Golang does print right type -- >> **S1* and **S2* >> >> Then I try type switch >> >> switch *LoopedItem*.(type){ >> case *S1: >> run(*LoopedItem*.(*S1)) >> case *S2: >> run(*LoopedItem*.(*S2)) >> } >> >> Everything goes on well. >> >> >> *I wonder why I can't use *LoopedItem* (as StringI interface) as run >> function's argument,but *LoopedItem*.(*TypePointer*) (as struct type >> pointer) to the run function.* >> >> >> >> Here is the source code >> >> >> #### firstInter.go #### >> >> /*my first interface*/ >> package firstInter >> >> import ( >> "fmt" >> "strconv" >> ) >> >> // interface with Get() and Push() method >> type StringI interface { >> Get() string >> Push(string) >> String() string >> } >> >> // type S1, store a int value >> type S1 struct { >> I int >> } >> >> // S1's Get method >> // return the int value it stored >> func (s *S1) Get() string { >> return strconv.Itoa(s.I) >> } >> >> // S1's Push method >> // put new value into S1 >> func (s *S1) Push(a string) { >> num, err := strconv.Atoi(a) >> if err == nil { >> s.I = num >> } >> } >> >> // S1's String method >> // for fmt >> func (s *S1) String() string { >> return strconv.Itoa(s.I) >> } >> >> // type S2, store a string value >> type S2 struct { >> S string >> } >> >> // S2's Get method >> // return the string value it stored >> func (s *S2) Get() string { >> return s.S >> } >> >> // S2's Push method >> // put new value into S2 >> func (s *S2) Push(a string) { >> s.S = a >> } >> >> // S2's String method >> // for fmt >> func (s *S2) String() string { >> return s.S >> } >> >> // function to run every method >> // StringI interface signatured >> func run(tI StringI) { >> fmt.Printf("%v\n", tI.Get()) >> tI.Push("3") >> fmt.Printf("%v\n", tI.Get()) >> } >> >> >> #### firstInter_test.go #### >> >> // firstInter package Unit Testing >> package firstInter >> >> import ( >> //"fmt" >> ) >> >> var tI StringI >> >> var s1 *S1 = &S1{1} >> var s2 *S2 = &S2{"???"} >> var l []interface{} = []interface{}{s1, s2} >> >> func Example_InterFace() { >> for _, item := range l { >> // something wrong here >> // run(item) >> // fmt.Printf("%T\n", item) >> switch item.(type) { >> case *S1: >> run(item.(*S1)) >> case *S2: >> run(item.(*S2)) >> } >> } >> // Output: >> // 1 >> // 3 >> // ??? >> // 3 >> } >> >> -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
