Mixed named and unnamed function parameters

I have this function for authenticating JWT tokens (not middleware), which says:

package main

import (
"net/http"
"log"
"fmt"
"github.com/dgrijalva/jwt-go"
)

func ValidateToken(w http.ResponseWriter, r *http.Request) *jwt.Token {

//parse token
token, err := jwt.ParseFromRequest(r, func(token *jwt.Token) (interface{}, err error) {
	return VerifyKey, nil
})

//validate token
if err != nil {

	switch err.(type) {

	//something went wrong during validation
	case *jwt.ValidationError:
		vErr := err.(*jwt.ValidationError)

		switch vErr.Errors {

		case jwt.ValidationErrorExpired:
			w.WriteHeader(http.StatusUnauthorized)
			fmt.Fprintln(w, "Token expired")
			return nil

		default:
			w.WriteHeader(http.StatusInternalServerError)
			fmt.Fprintln(w, "Error parsing token")
			log.Printf("Validation error: %v\n", err)
			return nil
		}


	//something else went wrong
	default:
		w.WriteHeader(http.StatusInternalServerError)
		fmt.Fprintln(w, "Error parsing token")
		log.Printf("Validation error: %v\n", err)
		return nil
	}

}

return token

}

Then, in my handlers, I call this function to get the token and check if it is valid using the Valid property in the JWT Token struct. However, when I run the web server, I get an error on line 13, saying:

Mixed named and unnamed function parameters

Line 13 is the jwt.ParseFromRequest() call. Any thoughts on what I am doing wrong? I am new to Go.

token, err := jwt.ParseFromRequest(r, func(token *jwt.Token) (interface{}, err error)

Your function here returns two parameters, an interface, and and error.

You need to name BOTH like ( x interface{}, err error )

or

You need to name NEITHER like ( interface{}, error )

because,

What you have there right now is a parameter list of two error type parameters.

Like when you say:

var x, y, z int

you have a list of ints, you wrote that you have 2 comma-separated variables of type error named interface{} and err. The compiler knows interface{} is a stupid name for an error variable, and is pointing out that you need a variable for the first (what it presumes is really a) type, or you should ditch the word err.

You are defining a function inline (of type jwt.Keyfunc), but not binding it to anything. If VerifyKey is of type jwt.Keyfunc, then you can just change line 13 to

token, err := jwt.ParseFromRequest(r, VerifyKey)

the same error can also occur if you forgot , in between the arguments list.

func someFunc(a string, b string c int) {}       // between string and c