为什么go编译器说一个结构在满足时不满足一个接口？

Question

I can see in scanner.go that the struct has an error method.

// A SyntaxError is a description of a JSON syntax error.
type SyntaxError struct {
    msg    string // description of error
    Offset int64  // error occurred after reading Offset bytes
}

func (e *SyntaxError) Error() string { return e.msg }

But the compiler tells me this:

api/errors.go:24: impossible type switch case: err (type error) cannot have dynamic type json.SyntaxError (missing Error method) when trying to do a switch case on type

func myFunction(err error) {
    switch err.(type) {
        case validator.ErrorMap, json.SyntaxError:
        response.WriteErrorString(http.StatusBadRequest, "400: Bad Request")
//etc       

Why does this not compile? Because the struct has the Error method.

Answer 1

It turns out that func (e *SyntaxError) Error() string { return e.msg } is a method for the pointer, whereas I am looking for the method on a value. I've managed to solve the problem by doing *json.SyntaxError to refer to a pointer.