tryParse static method

Implementation

static Quaternion? tryParse(String source) {
  final parts = numberAndUnitExtractor
      .allMatches(source.replaceAll(' ', ''))
      .where((match) => match.start < match.end)
      .toList();
  if (parts.isEmpty) {
    return null;
  }
  num w = 0, x = 0, y = 0, z = 0;
  final seen = <String>{};
  for (final part in parts) {
    final numberString = part.group(1) ?? '';
    final number = num.tryParse(numberString);
    final unitString = part.group(4) ?? '';
    final unit = unitString.toLowerCase();
    if (seen.contains(unit)) {
      return null; // repeated unit
    }
    if (unit == '' && number != null) {
      w = number;
    } else if (numberString.isEmpty || number != null) {
      switch (unit) {
        case 'i':
          x = number ?? 1;
        case 'j':
          y = number ?? 1;
        case 'k':
          z = number ?? 1;
        default:
          return null; // invalid unit
      }
    } else {
      return null; // parse error
    }
    seen.add(unit);
  }
  return Quaternion(w, x, y, z);
}