英文:
Golang update pass by reference value
问题
我正在调用一个函数来执行 HTTP 请求，该函数使用两个按引用传递的参数。我将 []byte 传递给 v 接口。我希望函数能够更新 v 接口的引用值。响应体是一个字符串，我想将字符串值传递给 v 接口。然而，尝试了很多方法都没有成功。
以下是代码，你可以看到我在声明中将 byts 声明为 v.(*[]byte)，以便使 v 更新为响应体的字符串值。但它不起作用。v 总是 nil。请建议任何方法，使 v 可以更新为字符串值。
func (s *BackendConfiguration) Do(req *http.Request, v interface{}) error {
res, err := s.HTTPClient.Do(req)
defer res.Body.Close()
resBody, err := ioutil.ReadAll(res.Body)
if v != nil {
byts, ok := v.(*[]byte)
if len(resBody) > 0 {
byts = append(byts, resBody...)
return nil
}
}
return nil
}
英文:
I am calling a function to do a http request, two pass by reference parameter is used for the function. I pass the []byte to v interface. I want the function to update the v interface reference value. The response body is a string, I want to pass the string value to v interface. However, tried many ways but not success.
Here is the code, you can see I declare byts as v.(*[]byte) in order to make v updated with the string value of response body. But it does not work. The v is always nil. Please suggest any way to make v can be updated with the string value.
func (s *BackendConfiguration) Do(req *http.Request, v interface{}) error {
res, err := s.HTTPClient.Do(req)
defer res.Body.Close()
resBody, err := ioutil.ReadAll(res.Body)
if v != nil {
byts, ok := v.(*[]byte)
if len(resBody) > 0 {
byts = append(byts, resBody...)
return nil
}
}
}
return nil
}
答案1
得分: 10
这段代码无法正常工作的主要原因是因为你在考虑"按引用调用"的概念，而这在Go语言中是完全不被支持的。在Go语言中，一切都是按值传递的，一旦你明确了什么是字节切片、字节切片的指针、包装在接口中的字节切片的指针、从接口中提取的字节切片指针的副本等等，你就会明白如何更新指向字节切片的指针所指向的值。
package main
import "fmt"
func f(v interface{}) {
pbs := v.(*[]byte)
*pbs = append(*pbs, []byte{9,8,7}...)
}
func main() {
bs := []byte{1,2,3}
pbs := &bs
var v interface{} = pbs
f(v)
fmt.Printf("%v\n", *pbs)
}
英文:
Well, the main reason this does not work is because you think of "call by reference", a concept completely unknown to Go. Absolutely everything is called by value in Go and once you spell out what is a byte slice, a pointer to a byte slice, a pointer to byte slice wrapped inside an interface, a copy of the pointer to a byte slice extracted from the interface, and so on you'll see how to update the value the pointer to byte slice points to:
package main
import "fmt"
func f(v interface{}) {
pbs := v.(*[]byte)
*pbs = append(*pbs, []byte{9,8,7}...)
}
func main() {
bs := []byte{1,2,3}
pbs := &bs
var v interface{} = pbs
f(v)
fmt.Printf("%v\n", *pbs)
}
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