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std::random...ess_iterator(3)  C++ Standard Libary std::random...ess_iterator(3)

NAME
     std::random_access_iterator - std::random_access_iterator

Synopsis
	Defined in header <iterator>
	template< class I >

	    concept random_access_iterator =
		std::bidirectional_iterator<I> &&
		std::derived_from</*ITER_CONCEPT*/<I>,
	std::random_access_iterator_tag> &&
		std::totally_ordered<I> &&
		std::sized_sentinel_for<I, I> &&
		requires(I  i,	const  I j, const std::iter_difference_t<I> n) {
     (since C++20)
		    { i += n } -> std::same_as<I&>;
		    { j +  n } -> std::same_as<I>;
		    { n +  j } -> std::same_as<I>;
		    { i -= n } -> std::same_as<I&>;
		    { j -  n } -> std::same_as<I>;
		    {  j[n]  } -> std::same_as<std::iter_reference_t<I>>;

		};

	The concept  random_access_iterator  refines  bidirectional_iterator  by
     adding support
	for  constant time advancement with the +=, +, -=, and - operators, con-
     stant time
	computation of distance with -, and array notation with subscripting [].

Notes
	Unlike	the  LegacyRandomAccessIterator  requirements,	the   random_ac-
     cess_iterator
	concept does not require dereference to return an lvalue.

Example
	Demonstrates  a  possible implementation of std::distance via C++20 con-
     cepts.

     // Run this code

      #include <iterator>

      namespace cxx20
      {
	  template<std::input_or_output_iterator Iter>
	  constexpr std::iter_difference_t<Iter> distance(Iter first, Iter last)
	  {
	      if constexpr(std::random_access_iterator<Iter>)
		  return last - first;
	      else
	      {
		  std::iter_difference_t<Iter> result{};
		  for (; first != last; ++first)
		      ++result;
		  return result;
	      }
	  }
      }

      int main()
      {
	  static constexpr auto il = {3, 1, 4};

	  static_assert(std::random_access_iterator<decltype(il.begin())> &&
			cxx20::distance(il.begin(), il.end()) == 3 &&
			cxx20::distance(il.end(), il.begin()) == -3);
      }

See also
	bidirectional_iterator specifies that a forward_iterator is  a	bidirec-
     tional
	(C++20) 	       iterator, supporting movement backwards
			       (concept)
	contiguous_iterator    specifies that a random_access_iterator is a con-
     tiguous
	(C++20) 	       iterator, referring to elements that are contigu-
     ous in memory
			       (concept)

http://cppreference.com 	   2024.06.10	   std::random...ess_iterator(3)
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