从函数返回多个值

Question

I have this function:

func GetBasicAuth(w http.ResponseWriter, r *http.Request) (string, error) {
    secret, _, ok := r.BasicAuth()
    if !ok {
        return "", err //is this right?
    }
    return secret, nil
}

I've had to declare that the function will return a string and an error but in reality it will return one or the other. If the BasicAuth function wasn't ok then I have no string to return so what do I do here - just send an empty string? This seems weird!

Answer 1

Unless documented otherwise (e.g. io.Reader), it's normal for Go functions/methods returning a, b, c, …, error to expect that if err != nil that all other returned values are undefined and should not be used/examined. It's usual (but not required) that when returning an error the function/method uses whatever the zero value is for those other return values.

As mentioned, some functions/methods such as an io.Reader's Read(p []byte) (n int, err error) explicitly state other behaviour:

Callers should always process the n > 0 bytes returned before considering the error err.

And any functions/methods you create that return useful values even in the case of (some) errors should probably explicitly state that.