package errhttp type NotExtended interface { ServerError NotExtended() } type internalNotExtended struct { err error } func NotExtendedWrap(err error) error { return internalNotExtended{ err:err, } } func (receiver internalNotExtended) Error() string { return receiver.err.Error() } func (receiver internalNotExtended) Err() error { return receiver.err } func (internalNotExtended) ServerError() { // Nothing here. } func (internalNotExtended) NotExtended() { // Nothing here. }