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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 ax i < (last - first) / 2.
	2) Same as (1), but uses r as the range, as if using ranges::begin(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 calling
     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 inhib-
     ited.

	In practice, they may be implemented as function objects, or  with  spe-
     cial 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 itera-
     tor 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 << " a ";
	  std::ranges::reverse(s.begin(), s.end());
	  std::cout << s << " a ";
	  std::ranges::reverse(s);
	  std::cout << s << " a ";

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

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