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4631. Post-increment/decrement operators of reverse_iterator and simd-iterator should be defaulted

Section: 24.5.1.2 [reverse.iterator], 29.10.6 [simd.iterator] Status: New Submitter: Jiang An Opened: 2026-10-26 Last modified: 2026-10-26

Priority: Not Prioritized

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Discussion:

Due to P3668R4, postfix forms of operator++ and operator-- can be defaulted since C++29. And P3785R1 made most of such default-able operators defaulted.

However, there're currently still a few default-able operators that are not defaulted, namely those of reverse_iterator and simd-iterator.

Proposed resolution:

This wording is relative to N5054.

1. Modify 24.5.1.2 [reverse.iterator] as indicated:

   […]
       constexpr reverse_iterator& operator++();
       constexpr reverse_iterator  operator++(int) = default;
       constexpr reverse_iterator& operator--();
       constexpr reverse_iterator  operator--(int) = default;
   […]
   

2. Modify 24.5.1.7 [reverse.iter.nav] as indicated:

   […]

   constexpr reverse_iterator operator++(int);
   

   -5- Effects: As if by:

   reverse_iterator tmp = *this;
   --current;
   return tmp;
   

   […]

   constexpr reverse_iterator operator--(int);
   

   -8- Effects: As if by:

   reverse_iterator tmp = *this;
   ++current;
   return tmp;
   

   […]

3. Modify 29.10.6 [simd.iterator] as indicated:

   […]
       constexpr simd-iterator& operator++();
       constexpr simd-iterator operator++(int) = default;
       constexpr simd-iterator& operator--();
       constexpr simd-iterator operator--(int) = default;
       constexpr reverse_iterator& operator++();
   […]
   

   […]

   constexpr simd-iterator operator++(int);
   

   -5- Effects: Equivalent to:

   simd-iterator tmp = *this;
   *this += 1;
   return tmp;
   

   […]

   constexpr simd-iterator operator--(int);
   

   -7- Effects: Equivalent to:

   simd-iterator tmp = *this;
   *this -= 1;
   return tmp;
   

   […]