Meaning of underscore in a Go function parameter

Question

Came accross the below function here. I noticed the last parameter is identified with _. What is the intent of this pattern?

func Index(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
    fmt.Fprint(w, "Welcome!\n")
}

Answer 1

It means "ignore that parameter", the reason that they still need the last parameter here is because they want to pass it as type Handle to the function GET, which has the signature:

type Handle func(http.ResponseWriter, *http.Request, Params)

If you simply pass something like func Index(w http.ResponseWriter, r *http.Request) it will not be treated as type Handle.

Answer 2

_ is the blank identifier. It's in the signature to show that the value doesn't get used, so the signature will still match the methods of the interface.