Proposed resolution:

This wording is relative to N4892.

1. Modify [move.iterators], class template move_iterator synopsis, as indicated:

   […]
   constexpr const iterator_type& base() const & noexcept;
   constexpr iterator_type base() &&;
   […]
   

2. Modify [move.iter.op.conv] as indicated:

   constexpr const Iterator& base() const & noexcept;
   

   -1- Returns: current.

3. Modify [counted.iterator], class template counted_iterator synopsis, as indicated:

   […]
   constexpr const I& base() const & noexcept;
   constexpr I base() &&;
   […]
   

4. Modify [counted.iter.access] as indicated:

   constexpr const I& base() const & noexcept;
   

   -1- Effects: Equivalent to: return current;

5. Modify [range.filter.iterator] as indicated:

   […]
   constexpr const iterator_t<V>& base() const & noexcept;
   constexpr iterator_t<V> base() &&;
   […]
   

   […]

   constexpr const iterator_t<V>& base() const & noexcept;
   

   -5- Effects: Equivalent to: return current_;

6. Modify [range.transform.iterator] as indicated:

   […]
   constexpr const iterator_t<Base>& base() const & noexcept;
   constexpr iterator_t<Base> base() &&;
   […]
   

   […]

   constexpr const iterator_t<Base>& base() const & noexcept;
   

   -5- Effects: Equivalent to: return current_;

7. Modify [range.lazy.split.outer.value] as indicated:

   […]
   constexpr inner-iterator<Const> begin() const;
   constexpr default_sentinel_t end() const noexcept;
   […]
   

   […]

   constexpr default_sentinel_t end() const noexcept;
   

   -3- Effects: Equivalent to: return default_sentinel;

8. Modify [range.lazy.split.inner] as indicated:

   […]
   constexpr const iterator_t<Base>& base() const & noexcept;
   constexpr iterator_t<Base> base() &&;
   […]
   

   […]

   constexpr const iterator_t<Base>& base() const & noexcept;
   

   -3- Effects: Equivalent to: return i_.current;

9. Modify [range.elements.iterator] as indicated:

   […]
   constexpr const iterator_t<Base>& base() const& noexcept;
   constexpr iterator_t<Base> base() &&;
   […]
   

   […]

   constexpr const iterator_t<Base>& base() const& noexcept;
   

   -6- Effects: Equivalent to: return current_;

[ 2021-10-14 Approved at October 2021 virtual plenary. Status changed: Voting → WP. ]

[ 2021-09-24; Reflector poll ]

Set status to Tentatively Ready after seven votes in favour during reflector poll.

LWG 3391 and 3533 changed some iterators' base() const & from returning value to returning const reference, which also prevents them from throwing exceptions, we should add noexcept for them. Also, lazy_split_view::outer-iterator::value_type::end() can be noexcept since it only returns default_sentinel.