英文:
Parameter passing in Go
问题
假设我有一个类型为http.HandleFunc的方法。
type HandlerFunc func(ResponseWriter, *Request)
我想将它包装在另一个相同类型的方法周围，类似于这样：
func MyWrapper(res http.ResponseWriter, req *http.Request) {// 做一些事情AnotherMethod(res, req) // <- 问题指的是这一行// 做更多的事情}func AnotherMethod(res http.ResponseWriter, req *http.Request) {// 主要逻辑}
如果我理解正确的话，当我调用AnotherMethod(res, req)时，我正在传递一个（值的）res的__副本__给AnotherMethod，这意味着这个对象现在在内存中被复制了。
有没有办法我可以传递一个指向res的__指针__给AnotherMethod，然后在那里解引用，以避免复制res的值？或者我理解错了什么？
（在AnotherMethod内部使用指向（值的）res的指针是行不通的，因为http.ResponseWriter中所有方法的接收者都是值，而不是指针）
英文:
Suppose I have a method of type http.HandleFunc
type HandlerFunc func(ResponseWriter, *Request)
And I want to wrap it around another method of the same type, somewhat like this:
func MyWrapper(res http.ResponseWriter, req *http.Request) {// do stuffAnotherMethod(res, req) // <- question refers to this line// do more stuff}func AnotherMethod(res http.ResponseWriter, req *http.Request) {// main logic}
If I'm getting this right; when I call AnotherMethod(res, req) I'm passing a copy of (the value of) res to AnotherMethod, meaning that this object is now duplicated in memory.
Is there a way I could pass a pointer to res to AnotherMethod and then dereference there, in order to not copy the value of res? or am I not understanding something?
(Working with a pointer to (the value of) res inside AnotherMethod won't work because the receivers of all methods in http.ResponseWriter are values and not pointers)
答案1
得分: 5
http.ResponseWriter 是一个接口类型。这意味着它可以是引用类型或值类型，取决于底层类型是什么以及它如何实现接口。
在这种情况下，res 是未导出类型 *http.response 的一个实例。正如你所见，它是一个指针类型，这意味着你可以传递它而不创建整个结构的副本。
要查看接收到的接口值内部保存的真实类型，你可以这样做：fmt.Printf("%T\n", res)。它应该打印出：*http.response。
关于 Go 中接口类型的工作原理的更多信息，我建议阅读有关该主题的Go 规范。
英文:
http.ResponseWriter is an interface type. Which means it can be both a reference or value type, depending on what the underlying type is and how it implements the interface.
In this case, res is an instance of the unexported type *http.response. As you can see, it is a pointer type, which means you can pass it around without creating a copy of the whole structure.
To see what real type is held inside an interface value you are receiving, you can do this: fmt.Printf("%T\n", res). It should print: *http.resonse.
For more information on how interface types work in Go, I recommend reading the Go specification on the subject.
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