How to model Go bindings to C structs that use unions? -

i'm writing go wrapper libfreefare. api of libfreefare contains following function:

struct mifare_desfire_file_settings {     uint8_t file_type;     uint8_t communication_settings;     uint16_t access_rights;     union {     struct {         uint32_t file_size;     } standard_file;     struct {         int32_t lower_limit;         int32_t upper_limit;         int32_t limited_credit_value;         uint8_t limited_credit_enabled;     } value_file;     struct {         uint32_t record_size;         uint32_t max_number_of_records;         uint32_t current_number_of_records;     } linear_record_file;     } settings; };  int      mifare_desfire_get_file_settings (mifaretag tag, uint8_t file_no, struct mifare_desfire_file_settings *settings); 

what ideomatic solution wrapping such function? if struct mifare_desfire_file_settings wouldn't contain unions, wrapper this:

type desfirefilesettings struct {     // fields exported, no methods }  func (t desfiretag) filesettings(fileno byte) (desfirefilesettings, error) 

how should proceed?

you need consider how update fields in union. obviously, can't let users without validation. inconsistent updates. consider doing this:

package mifare  const (     mdftstandardatafile            = 0x00     mdftbackupdatafile             = 0x01     mdftvaluefilewithbackup        = 0x02     mdftlinearrecordfilewithbackup = 0x03     mdftcyclicrecordfilewithbackup = 0x04 )  type standardfile struct {     filesize uint32 }  type valuefile struct {     lowerlimit           int32     upperlimit           int32     limitedcreditvalue   int32     limitedcreditenabled uint8 }  type linearrecordfile struct {     record_size            uint32     maxnumberofrecords     uint32     currentnumberofrecords uint32 }  type desfirefilesettings struct {     filetype              uint8     communicationsettings uint8     accessrights          uint16     settings              struct {         standardfile         valuefile         linearrecordfile     } }  func (fs *desfirefilesettings) standardfile() (standardfile, error) {     // if not valid filetype, return error     return fs.settings.standardfile, nil }  func (fs *desfirefilesettings) setstandardfile(standardfile standardfile) error {     // if not valid filetype, return error     fs.settings.standardfile = standardfile     return nil }  func (fs *desfirefilesettings) valuefile() (valuefile, error) {     // if not valid filetype, return error     return fs.settings.valuefile, nil }  func (fs *desfirefilesettings) setvaluefile(valuefile valuefile) error {     // if not valid filetype, return error     fs.settings.valuefile = valuefile     return nil }  func (fs *desfirefilesettings) linearrecordfile() (linearrecordfile, error) {     // if not valid filetype, return error     return fs.settings.linearrecordfile, nil }  func (fs *desfirefilesettings) setlinearrecordfile(linearrecordfile linearrecordfile) error {     // if not valid filetype, return error     fs.settings.linearrecordfile = linearrecordfile     return nil }