pattern static method

String? Function(String?) pattern(
  1. RegExp regex, [
  2. String? message
])

Pattern match

Implementation

static String? Function(String?) pattern(RegExp regex, [String? message]) {
  return (value) {
    if (value == null || value.isEmpty) return null;
    if (!regex.hasMatch(value)) {
      return message ?? 'Invalid format';
    }
    return null;
  };
}