http.ResponseWriter as pointer or value?

[Nguyên Nguyễn Văn Cao]

Sure this is a newbie stupid question, but I hope some one can give me more detail!

I have a simple code that in defaultHandler it call sub handler Test1 and Test2 as below:

___________________________

func defaultHandler(w http.ResponseWriter, r *http.Request) {

Test1(&w)

Test2(w)

}

func main() {

http.HandleFunc("/", defaultHandler)

http.ListenAndServe(":8080", nil)

}

func Test1(w* http.ResponseWriter) {

fmt.Fprintf(*w, "test1")

}

func Test2(w http.ResponseWriter) {

fmt.Fprintf(w, "test2")

}

___________________________

w http.ResponseWriter is a Interface? And "w" is a instance of an Interface???

In my case, Test function should recive a pointer or a copy of "w"? Why?

[Shaban Naasso]

interface means simply that it implements all the functions that are declared in the interface

so these are the functions in the interface

type ResponseWriter interface {
    Header() Header
    Write([]byte) (int, error)
    WriteHeader(int)
}

if something implements these 3 functions then it can be used for ResponseWriting

one other detail to help you understand it.

the Write([]byte) (int, error) function you see is actually a function in the io.Writer interface

this means it's a ResponseWriter and also an io.Writer and you can use it for all things you can use these types for.

if you are interested in what this actually means take a look at this post it explains quite nicely how you can work with io to add gzip handling to a http.ResponseWriter's output

http://nf.id.au/roll-your-own-gzip-encoded-http-handler

[Shaban Naasso]

after reading my post i thought i try to explain that interface thing better look at following example:

type Fighter interface{

 Fight() bool //finding out if all consitions are met to actually fight

}

type Rebel struct{

 Idelogy string

}

type Mercenary struct{

 Payment int

}

func(r *Rebel)Fight()bool{

 // will fight if he is inclined to do so

 return r.Ideology=="Militaristic"

}

func(m *MercenaryFight()bool{

 // will fight if he gets more than 2000 Dollar 

 return m.Payment > 2000

}

func WillHeFight(fs Fighter)bool{

 return fs.Fight()

}

this is not a complete Program it's just to see how an arbitrary data structure by implementing functions can be used as a certain type

in this case Fighter.

[Nguyên Nguyễn Văn Cao]

Thank Shaban Naasso for your explanation about interface :)

Vào 19:37:00 UTC+7 Thứ bảy, ngày 28 tháng tư năm 2012, Shaban Naasso đã viết: