func (m *Mapping) Source() (string, int64) {
	if m.f == nil {
		return "", 0
	}
	return m.f.Name(), m.off
}
func (m *Mapping) Source() (string, int64) {
	if m.f == nil {
		return "", 0
	}
	return m.f.Name(), m.off
}
func ( m * Mapping ) Source ( ) ( string , int64 ) { if m . f == nil { return " " , 0 } return m . f . Name ( ) , m . off }
// Source returns the backing file and offset for the mapping, or "", 0 if none.
Source returns the backing file and offset for the mapping or 0 if none .