2016-06-25 06:20
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func main() {
    http.HandleFunc("/", handler)

func handler(w http.ResponseWriter, r http.Request) {
    // I never declared, initialized or passed w and r. How does this function get access to them?

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  func main(){
 http.HandleFunc(“ /”,handler)
} \  n 
func handler(w http.ResponseWriter,r http.Request){
 //我从未声明,初始化或传递w和r。 此功能如何访问它们?
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2条回答 默认 最新

  • doushenxu7294 2016-06-25 18:32

    http.HandleFunc knows its given input parms and that 2nd parm will have its own input parms (w http.ResponseWriter, r http.Request) ... so w and r are setup by http.HandleFunc which after it registers func handler as a callback it then invokes passing in w and r ... so responsibility is given to calling context not inside the callback definition itself

    Its a worth while exercise to write your own such pair of functions where one is a callback passed into and invoked by other function ... this pattern is orthogonal to golang and is a pervasive tool across languages

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  • duanhui5344 2016-06-25 06:24

    It's the magic of golang and the http package. No just kiding.

    In fact http.HandleFunc will do this for you, so when a request will reach your webservice with a matching url, then golang http package will call your handler with w and r ready to be used.

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