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std::ranges::reverse(3)	      C++ Standard Libary      std::ranges::reverse(3)

NAME
       std::ranges::reverse - std::ranges::reverse

Synopsis
	  Defined in header <algorithm>
	  Call signature
	  template< std::bidirectional_iterator	I, std::sentinel_for<I>	S >

	  requires					    std::permutable<I>
       (1) (since C++20)
	  constexpr I

	      reverse( I first,	S last );
	  template< ranges::bidirectional_range	R >

	  requires			std::permutable<ranges::iterator_t<R>>
       (2) (since C++20)
	  constexpr ranges::borrowed_iterator_t<R>

	      reverse( R&& r );

	  1) Reverses the order	of the elements	in the range [first, last).
	  Behaves  as if applying ranges::iter_swap to every pair of iterators
       first + i, last
	  - i -	1 for each integer i, where 0  i < (last - first) / 2.
	  2) Same as (1), but uses r as	the range,  as	if  using  ranges::be-
       gin(r) as first and
	  ranges::end(r) as last.

	  The  function-like  entities	described  on this page	are niebloids,
       that is:

	    * Explicit template	argument lists cannot be specified when	 call-
       ing any of them.
	    * None of them are visible to argument-dependent lookup.
	    *  When  any of them are found by normal unqualified lookup	as the
       name to the left
	      of the function-call operator, argument-dependent	lookup is  in-
       hibited.

	  In  practice,	 they  may be implemented as function objects, or with
       special compiler
	  extensions.

Parameters
	  first, last -	the range of elements to reverse
	  r	      -	the range of elements to reverse

Return value
	  An iterator equal to last.

Complexity
	  Exactly (last	- first) / 2 swaps.

Notes
	  Implementations (e.g.	MSVC STL) may enable  vectorization  when  the
       iterator	type
	  models contiguous_iterator and swapping its value type calls neither
       non-trivial
	  special member function nor ADL-found	swap.

Possible implementation
	  See also implementations in libstdc++	and MSVC STL.

	  struct reverse_fn
	  {
	      template<std::bidirectional_iterator I, std::sentinel_for<I> S>
	      requires std::permutable<I>
	      constexpr	I operator()(I first, S	last) const
	      {
		  auto last2 {ranges::next(first, last)};
		  for (auto tail {last2}; !(first == tail or first == --tail);
       ++first)
		      ranges::iter_swap(first, tail);
		  return last2;
	      }

	      template<ranges::bidirectional_range R>
	      requires std::permutable<ranges::iterator_t<R>>
	      constexpr	ranges::borrowed_iterator_t<R>
		  operator()(R&& r) const
	      {
		  return (*this)(ranges::begin(r), ranges::end(r));
	      }
	  };

	  inline constexpr reverse_fn reverse {};

Example
       // Run this code

	#include <algorithm>
	#include <array>
	#include <iostream>
	#include <string>

	int main()
	{
	    std::string	s {"ABCDEF"};
	    std::cout << s << "	 ";
	    std::ranges::reverse(s.begin(), s.end());
	    std::cout << s << "	 ";
	    std::ranges::reverse(s);
	    std::cout << s << "	 ";

	    std::array a {1, 2,	3, 4, 5};
	    for	(auto e	: a)
		std::cout << e << ' ';
	    std::cout << " ";
	    std::ranges::reverse(a);
	    for	(auto e	: a)
		std::cout << e << ' ';
	    std::cout << '\n';
	}

Output:
	ABCDEF	FEDCBA	ABCDEF	1 2 3 4	5  5 4 3 2 1

See also
	  ranges::reverse_copy creates a copy of a range that is reversed
	  (C++20)	       (niebloid)
	  ranges::reverse_view	a  view	that iterates over the elements	of an-
       other bidirectional
	  views::reverse       view in reverse order
	  (C++20)	       (class template)	(range adaptor object)
	  reverse	       reverses	the order of elements in a range
			       (function template)

http://cppreference.com		  2024.06.10	       std::ranges::reverse(3)

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