combineResult<T extends Object> function

Result<List<T>> combineResult<T extends Object>(Iterable<Result<T>> results, { @noFutures Err<List<T>> onErr(List<Result<T>> allResults)?, })

Combines an iterable of Results into one containing a list of their values.

If any Result is an Err, applies the onErr function to combine errors.

Implementation

Result<List<T>> combineResult<T extends Object>(
  Iterable<Result<T>> results, {
  @noFutures Err<List<T>> Function(List<Result<T>> allResults)? onErr,
}) {
  // Fast path: when no aggregating error handler is configured we never need
  // to keep the original list around — iterate the input directly and
  // propagate the first Err immediately. Skips one List allocation per call.
  if (onErr == null) {
    final successes = <T>[];
    for (final result in results) {
      switch (result) {
        case Ok(value: final value):
          successes.add(value);
        case final Err err:
          return err.transfErr();
      }
    }
    return Ok(successes);
  }
  // Slow path: onErr wants the full original list, so materialize once.
  final asList = results.toList();
  final successes = <T>[];
  for (final result in asList) {
    switch (result) {
      case Ok(value: final value):
        successes.add(value);
      case final Err _:
        return onErr(asList);
    }
  }
  return Ok(successes);
}