description

# single property

E get single
override

Checks that this iterable has only one element, and returns that element.

Throws a StateError if `this` is empty or has more than one element. This operation will not iterate past the second element.

## Implementation

    E get single {
      // Note that this throws correctly if the queue is empty
      // because reading the element of the sentinel throws.
      if (identical(_sentinel._nextLink, _sentinel._previousLink)) {
        return _sentinel._nextLink!.element;
      }
      throw IterableElementError.tooMany();
    }