Why the request is a pointer variable? Why not a reference variable?

Question

I have been learning GO Lang for a month now. I have been coding in java for more than 4 years. In java the Request and Response both are object references. But, when it comes to GoLang the Response is a object reference and the Request is a Pointer Reference.

A reference, like a pointer, is an object that you can use to refer indirectly to another object. A reference declaration has essentially the same syntactic structure as a pointer declaration.

func hello(w http.ResponseWriter, r *http.Request) {
    io.WriteString(w, "Hello world!")
}

Apart from the readability perspective and the syntactic sugar is there any other intention behind using the Request as a pointer variable.

Adding to the above question the request here is an arbitrary pointer. i.e the request is not yet exists but the pointer is already referring to a memory location. Please throw some light if my understanding is wrong.

Answer 1

As correctly mentioned in many other answers here and elsewhere, ResponseWriter is an interface and the implications of this have beed described in detail in SO answers and blogs.

What I would like to address is what I feel is the big—and dangerous—misconception here, that the reason request is passed by "reference" (although such a thing does not really exist in Go) is that "we want to make changes to it visible to the server".

Quoting a couple of answers from other people:

[..]it's just a struct, and since we want to change this struct and have the web server see those changes, it has to be a pointer[..] SO

[..]changes to Request by the handler need to be visible to the server, so we’re only passing it by reference instead of by value [..] SO

This is wrong; in fact the docs explicitly warn against tampering with / mutating the request:

Except for reading the body, handlers should not modify the provided Request.

Quite the opposite, no? :-)

If you want to change the request, e.g. append a tracing header before passing it on to the next handler in a middleware chain you have to copy the request and pass the copied version down the chain.

Why use a pointer if we are explicitly telling people not to mutate the request? Performance, Request is a large struct and copying it can bring performance down, especially with long middleware chains in mind. The team had to strike a balance, definitely not an ideal solution, but the tradeoffs are clearly on the side of performance here (instead of API safety).