Code39Reader constructor
Creates a reader that can be configured to check the last character as a check digit, or optionally attempt to decode "extended Code 39" sequences that are used to encode the full ASCII character set.
@param usingCheckDigit if true, treat the last data character as a check digit, not data, and verify that the checksum passes. @param extendedMode if true, will attempt to decode extended Code 39 sequences in the text.
Implementation
Code39Reader([this._usingCheckDigit = false, this._extendedMode = false])
: _decodeRowResult = StringBuilder(),
_counters = List.filled(9, 0);