pattern function

@useResult Parser<String> pattern(String pattern, { String? message, bool ignoreCase = false, bool unicode = false, })

Returns a parser that accepts a single character of a given character set pattern provided as a string.

Characters match themselves. A dash - between two characters matches the range of those characters. A caret ^ at the beginning negates the pattern.

For example, the parser pattern('aou') accepts the character 'a', 'o', or 'u', and fails for any other input. The parser pattern('1-3') accepts either '1', '2', or '3'; and fails for any other character. The parser `pattern('^aou') accepts any character, but fails for the characters 'a', 'o', or 'u'.

If ignoreCase is set to true the pattern accepts lower and uppercase variations of its characters. If unicode is set to true unicode surrogate pairs are extracted and matched against the predicate.

Implementation

@useResult
Parser<String> pattern(
  String pattern, {
  String? message,
  bool ignoreCase = false,
  bool unicode = false,
}) {
  var input = pattern;
  final isNegated = input.startsWith('^');
  if (isNegated) input = input.substring(1);
  final inputs = ignoreCase
      ? [input.toLowerCase(), input.toUpperCase()]
      : [input];
  final parser = unicode ? _patternUnicodeParser : _patternParser;
  var predicate = optimizedRanges(
    inputs.expand((each) => parser.parse(each).value),
    unicode: unicode,
  );
  if (isNegated) {
    predicate = predicate is ConstantCharPredicate
        ? ConstantCharPredicate(!predicate.constant)
        : NotCharPredicate(predicate);
  }
  message ??=
      '[${toReadableString(pattern, unicode: unicode)}]'
      '${ignoreCase ? ' (case-insensitive)' : ''} expected';
  return CharacterParser(predicate, message, unicode: unicode);
}