pattern static method

String? Function(String?) pattern(
  1. RegExp regex, {
  2. String? message,
})

Returns a validator that checks against a regex pattern.

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;
  };
}