/// Einfaches Ergebnis-Typ für erwartbare Fehler (kein zusätzliches Paket).
sealed class Result<T, E> {
  const Result();

  const factory Result.success(T value) = Success<T, E>;
  const factory Result.failure(E error) = Failure<T, E>;

  bool get isSuccess => this is Success<T, E>;
  bool get isFailure => this is Failure<T, E>;

  /// Wert bei Erfolg, sonst `null`.
  T? get valueOrNull => switch (this) {
    Success<T, E>(:final value) => value,
    Failure<T, E>() => null,
  };

  /// Fehler bei Misserfolg, sonst `null`.
  E? get errorOrNull => switch (this) {
    Success<T, E>() => null,
    Failure<T, E>(:final error) => error,
  };

  R when<R>({
    required R Function(T value) success,
    required R Function(E error) failure,
  }) => switch (this) {
    Success<T, E>(:final value) => success(value),
    Failure<T, E>(:final error) => failure(error),
  };
}

final class Success<T, E> extends Result<T, E> {
  const Success(this.value);
  final T value;
}

final class Failure<T, E> extends Result<T, E> {
  const Failure(this.error);
  final E error;
}