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3817. Missing preconditions on forward_list modifiers

Section: 23.3.7.5 [forward.list.modifiers] Status: C++23 Submitter: Tomasz Kamiński Opened: 2022-11-08 Last modified: 2023-11-22

Priority: Not Prioritized

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Discussion:

This is resolution of GB-101 (23.3.7.5 [forward.list.modifiers] p12,15,20,21 Missing preconditions on forward_list modifiers).

Some of the modifiers to forward_list are special to that container and accordingly are not described in 23.2 [container.requirements]. Specifically, insert_after (iterator overload), insert_range_after and emplace_after do not verify that the value_type is Cpp17EmplaceConstructible from the appropriate argument(s). Furthermore insert_after (value overloads) are missing Cpp17CopyInsertable/Cpp17MoveInsertable requirements.

[Kona 2022-11-08; Move to Ready]

[Kona 2022-11-12; Correct status to Immediate]

[2022-11-12 Approved at November 2022 meeting in Kona. Status changed: Immediate → WP.]

Proposed resolution:

This wording is relative to N4917.

1. Modify 23.3.7.5 [forward.list.modifiers] as indicated:

   [Drafting note: emplace_front, push_front, and prepend_range are already covered by 23.2 [container.requirements]. ]

   iterator insert_after(const_iterator position, const T& x);
   

   -?- Preconditions: T is Cpp17CopyInsertable into forward_list. position is before_begin() or is a dereferenceable iterator in the range [begin(), end()).

   -?- Effects: Inserts a copy of x after position.

   -?- Returns: An iterator pointing to the copy of x.

   iterator insert_after(const_iterator position, T&& x);
   

   -6- Preconditions: T is Cpp17MoveInsertable into forward_list. position is before_begin() or is a dereferenceable iterator in the range [begin(), end()).

   -7- Effects: Inserts a copy of x after position.

   -8- Returns: An iterator pointing to the copy of x.

   iterator insert_after(const_iterator position, size_type n, const T& x);
   

   -9- Preconditions: T is Cpp17CopyInsertable into forward_list. position is before_begin() or is a dereferenceable iterator in the range [begin(), end()).

   -10- Effects: Inserts n copies of x after position.

   -11- Returns: An iterator pointing to the last inserted copy of x, or position if n == 0 is true.

   template<class InputIterator>	
     iterator insert_after(const_iterator position, InputIterator first, InputIterator last);
   

   -12- Preconditions: T is Cpp17EmplaceConstructible into forward_list from *first. position is before_begin() or is a dereferenceable iterator in the range [begin(), end()). Neither first nor last are iterators in *this.

   -13- Effects: Inserts copies of elements in [first, last) after position.

   -14- Returns: An iterator pointing to the last inserted element, or position if first == last is true.

   template<container-compatible-range<T> R>
     iterator insert_after(const_iterator position, R&& rg);
   

   -15- Preconditions: T is Cpp17EmplaceConstructible into forward_list from *ranges::begin(rg). position is before_begin() or is a dereferenceable iterator in the range [begin(), end()). rg and *this do not overlap.

   -16- Effects: Inserts copies of elements in range rg after position.

   -17- Returns: An iterator pointing to the last inserted element, or position if rg is empty.

   iterator insert_after(const_iterator position, initializer_list<T> il);
   

   -18- Effects: Equivalent to: return insert_after(position, il.begin(), il.end()).;

   -19- Returns: An iterator pointing to the last inserted element or position if il is empty.

   template<class... Args>	
     iterator emplace_after(const_iterator position, Args&&... args);
   

   -20- Preconditions: T is Cpp17EmplaceConstructible into forward_list from std::forward<Args>(args).... position is before_begin() or is a dereferenceable iterator in the range [begin(), end()).

   -21- Effects: Inserts an object of type value_type constructeddirect-non-list-initialized with value_type(std::forward<Args>(args)...) after position.

   -22- Returns: An iterator pointing to the new object.