anchor.diff:  library more.iterable.indexed;
  -
  -import 'dart:collection' show IterableBase;
   
   /// Returns a [Indexed] iterable
   ///
  
positive.code: ///
  ///     'a-1, b-2'
  ///
  Iterable<Indexed<E>> indexed<E>(Iterable<E> iterable, {int offset = 0}) {
    return IndexedIterable<E>(iterable, offset);
  }
  
  /// An indexed value.
  
negative.code:   @override
    String toString() => '$index: $value';
  }
  