firstError<ErrorType> method

ErrorType? firstError<ErrorType>(
  1. S subject
)

Runs the validator and returns the first error of the provided generic type

When supplied a type parameter the error list will be filtered to all errors that have the given type. This is handy when just error information is required.

Implementation

ErrorType? firstError<ErrorType>(S subject) {
  return this(subject).leftMap((errors) {
    final Iterable<ErrorType> filtered = errors.whereType();
    final list = filtered.toList();
    return list.isEmpty ? null : list.first;
  }).fold((l) => l, (r) => null);
}