| /// Marker interface for [Iterable] subclasses that have an efficient |
| /// [length] implementation. |
| |
| // @dart=2.9 |
| |
| abstract class EfficientLengthIterable<T> extends Iterable<T> { |
| const EfficientLengthIterable(); |
| |
| /// Returns the number of elements in the iterable. |
| /// |
| /// This is an efficient operation that doesn't require iterating through |
| /// the elements. |
| int get length; |
| } |
| |
| /// Creates errors throw by [Iterable] when the element count is wrong. |
| abstract class IterableElementError { |
| /// Error thrown thrown by, e.g., [Iterable.first] when there is no result. |
| static StateError noElement() => StateError("No element"); |
| |
| /// Error thrown by, e.g., [Iterable.single] if there are too many results. |
| static StateError tooMany() => StateError("Too many elements"); |
| |
| /// Error thrown by, e.g., [List.setRange] if there are too few elements. |
| static StateError tooFew() => StateError("Too few elements"); |
| } |