xdr/ledger_key.go
func (key *LedgerKey) SetOffer(account AccountId, id uint64) error {
	data := LedgerKeyOffer{account, Uint64(id)}
	nkey, err := NewLedgerKey(LedgerEntryTypeOffer, data)
	if err != nil {
		return err
	}

	*key = nkey
	return nil
}
func (key *LedgerKey) SetOffer(account AccountId, id uint64) error {
	data := LedgerKeyOffer{account, Uint64(id)}
	nkey, err := NewLedgerKey(LedgerEntryTypeOffer, data)
	if err != nil {
		return err
	}

	*key = nkey
	return nil
}
// SetOffer mutates `key` such that it represents the identity of the
// data entry owned by `account` and for offer `id`.