_, ok := r.(WriterTo)

// NopCloser returns a ReadCloser with a no-op Close method wrapping

// the provided Reader r.

// If r implements WriterTo, the returned ReadCloser will implement WriterTo

// by forwarding calls to r.

func NopCloser(r Reader) ReadCloser {

    if _, ok := r.(WriterTo); ok {

        return nopCloserWriterTo{r}

    }

    return nopCloser{r}

}