description

# single property Null safety

E single

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.

## Implementation

    E get single {
      if (_head == _tail) throw IterableElementError.noElement();
      if (length > 1) throw IterableElementError.tooMany();
      return _table[_head] as E;
    }