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std::random...ess_iterator(3) C++ Standard Libarystd::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,
       constant	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
       concepts.

       // 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	 bidi-
       rectional
	  (C++20)		 iterator, supporting movement backwards
				 (concept)
	  contiguous_iterator	  specifies that a random_access_iterator is a
       contiguous
	  (C++20)		 iterator, referring to	elements that are con-
       tiguous in memory
				 (concept)

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

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