Proposed resolution:

This wording is relative to N4971.

[Drafting Note: The proposed wording is similar to the specification in [vector.overview] p2 and suggests to simply strike [string.iterators] because it doesn't say anything new compared to [container.reqmts] and [container.rev.reqmts].

Alternatively, one could add a

Complexity: Constant.

paragraph to each function in [string.iterators], but that would be less clearer and would not explicitly say basic_string meets the reversible container requirements. ]

1. Modify [basic.string.general] as indicated:

   -2- A specialization of basic_string is a contiguous container ([container.reqmts]) and a reversible container ([container.rev.reqmts]).

   -3- In all cases, [data(), data() + size()] is a valid range, data() + size() points at an object with value charT() (a "null terminator"), and size() <= capacity() is true.

   namespace std {
     template<class charT, class traits = char_traits<charT>,
              class Allocator = allocator<charT>>
     class basic_string {
       […]
       // [string.iterators], iterators
       constexpr iterator begin() noexcept;
       constexpr const_iterator begin() const noexcept;
       constexpr iterator end() noexcept;
       constexpr const_iterator end() const noexcept;
     
       constexpr reverse_iterator rbegin() noexcept;
       constexpr const_reverse_iterator rbegin() const noexcept;
       constexpr reverse_iterator rend() noexcept;
       constexpr const_reverse_iterator rend() const noexcept;
     
       constexpr const_iterator cbegin() const noexcept;
       constexpr const_iterator cend() const noexcept;
       constexpr const_reverse_iterator crbegin() const noexcept;
       constexpr const_reverse_iterator crend() const noexcept;
     
       // [string.capacity], capacity
       […]
     };
     […]
   }
   

   […]

2. Remove subclause [string.iterators] in its entirety:

   23.4.3.4 Iterator support [string.iterators]

   constexpr iterator begin() noexcept;
   constexpr const_iterator begin() const noexcept;
   constexpr const_iterator cbegin() const noexcept;
   

   -1- Returns: An iterator referring to the first character in the string.

   […]

   constexpr reverse_iterator rend() noexcept;
   constexpr const_reverse_iterator rend() const noexcept;
   constexpr const_reverse_iterator crend() const noexcept;
   

   -4- Returns: An iterator which is semantically equivalent to reverse_iterator(begin()).

[ 2024-03-15; Reflector poll ]

Set priority to 3 after reflector poll.

Could harmonize with vector by saying: "A basic_string meets all of the requirements of a contiguous container ([container.reqmts]) and of a reversible container ([container.rev.reqmts])." It's not a sequence container (see LWG 718) but as per [container.alloc.reqmts] p1 it is allocator-aware (although it doesn't use construct and destroy).

Not comfortable removing the detailed descriptions for those members. We don't have the "Descriptions are only provided here for operations on [...] that are not described in one of these tables" wording that the containers have.

The complexity requirements for a reversible container ([container.rev.reqmts]) are that each function must have constant complexity. The corresponding member functions in [string.iterators] have no complexity requirements, and basic_string unintentionally is not a reversible container (unless the implementation coincidentally provides constant complexity member functions).