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3955. Add noexcept to several repeat_view[::iterator] member functions

Section: 25.6.5.2 [range.repeat.view], 25.6.5.3 [range.repeat.iterator] Status: New Submitter: Hewill Kang Opened: 2023-07-06 Last modified: 2023-10-30

Priority: 3

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Discussion:

Several member functions of repeat_view::iterator only operate on its integer member, indicating that they do not throw.

Similarly, repeat_view::size should also be noexcept since it just performs the integer conversion.

[2023-10-30; Reflector poll]

Set priority to 3 after reflector poll. Some votes for NAD. "The iterator changes violate the Lakos rule."

Proposed resolution:

This wording is relative to N4950.

1. Modify 25.6.5.2 [range.repeat.view], class template repeat_view synopsis, as indicated:

   namespace std::ranges {
     […]
     template<move_constructible T, semiregular Bound = unreachable_sentinel_t>
       requires (is_object_v<T> && same_as<T, remove_cv_t<T>> &&
                 (integer-like-with-usable-difference-type<Bound> ||
                  same_as<Bound, unreachable_sentinel_t>))
     class repeat_view : public view_interface<repeat_view<T, Bound>> {
     private:
       […]
     public:
       […]
   
       constexpr auto size() const noexcept requires (!same_as<Bound, unreachable_sentinel_t>);
     };
     […]
   }
   

   […]

   constexpr auto size() const noexcept requires (!same_as<Bound, unreachable_sentinel_t>);
   

   -9- Effects: Equivalent to: return to-unsigned-like(bound_);

2. Modify 25.6.5.3 [range.repeat.iterator], class repeat_view::iterator synopsis, as indicated:

   namespace std::ranges {
     template<move_constructible T, semiregular Bound>
       requires (is_object_v<T> && same_as<T, remove_cv_t<T>> &&
                 (integer-like-with-usable-difference-type<Bound> ||
                  same_as<Bound, unreachable_sentinel_t>))
     class repeat_view<T, Bound>::iterator {
     private:
      using index-type =                          // exposition only
         conditional_t<same_as<Bound, unreachable_sentinel_t>, ptrdiff_t, Bound>;
      const T* value_ = nullptr;                  // exposition only
      index-type current_ = index-type();         // exposition only
   
      constexpr explicit iterator(const T* value, index-type b = index-type());   // exposition only
   
     public:
       […]
       constexpr iterator& operator++() noexcept;
       constexpr iterator operator++(int) noexcept;
   
       constexpr const T& operator[](difference_type n) const noexcept;
   
       friend constexpr bool operator==(const iterator& x, const iterator& y) noexcept;
       friend constexpr auto operator<=>(const iterator& x, const iterator& y) noexcept;
   
       friend constexpr difference_type operator-(const iterator& x, const iterator& y) noexcept;
     };
   }
   

   […]

   constexpr iterator& operator++() noexcept;
   

   -5- Effects: Equivalent to:

   ++current_;
   return *this;
   

   constexpr iterator operator++(int) noexcept;
   

   -6- Effects: Equivalent to:

   auto tmp = *this;
   ++*this;
   return tmp;
   

   […]

   friend constexpr bool operator==(const iterator& x, const iterator& y) noexcept;
   

   -15- Effects: Equivalent to: return x.current_ == y.current_;

   friend constexpr auto operator<=>(const iterator&x, const iterator& y) noexcept;
   

   -16- Effects: Equivalent to: return x.current_ <=> y.current_;

   […]

   friend constexpr difference_type operator-(const iterator& x, const iterator& y) noexcept;
   

   -19- Effects: Equivalent to:

   return static_cast<difference_type>(x.current_) - static_cast<difference_type>(y.current_);