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/// Marker interface for [Iterable] subclasses that have an efficient
/// [length] implementation.
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");