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

NAME
     std::ranges::fill - std::ranges::fill

Synopsis
	Defined in header <algorithm>
	Call signature
	template< class T, std::output_iterator<const
	T&> O, std::sentinel_for<O> S > 			 (since C++20)
	constexpr O fill( O first, S last, const T&		 (until C++26)
	value );
	template< class O, std::sentinel_for<O> S, class
	T = std::iter_value_t<O> >

	requires std::output_iterator<O, const T&>		 (since C++26)

	constexpr O fill( O first, S last, const T&
	value );					 (1)
	template< class T, ranges::output_range<const
	T&>				     R				       >
     (since C++20)
	constexpr	       ranges::borrowed_iterator_t<R>		   fill(
     (until C++26)
	R&& r, const T& value );
	template< class R, class T =
	std::range_value_t<R> > 			     (2)

	requires	   ranges::output_range<R,	     const	     T&>
     (since C++26)

	constexpr ranges::borrowed_iterator_t<R> fill(
	R&& r, const T& value );

	1) Assigns the given value to the elements in the range [first, last).
	2) Same as (1), but uses r as the source 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  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 modify
	r	    - the range of elements to modify
	value	    - the value to be assigned

Return value
	An output iterator that compares equal to last.

Complexity
	Exactly last - first assignments.

Possible implementation
	struct fill_fn
	{
	    template<class   O,    std::sentinel_for<O>    S,	 class	  T    =
     std::iter_value_t<O>>
	    requires std::output_iterator<O, const T&>
	    constexpr O operator()(O first, S last, const T& value) const
	    {
		while (first != last)
		    *first++ = value;

		return first;
	    }

	    template<class R, class T = std::range_value_t<R>>
	    requires ranges::output_range<R, const T&>
	    constexpr  ranges::borrowed_iterator_t<R> operator()(R&& r, const T&
     value) const
	    {
		return (*this)(ranges::begin(r), ranges::end(r), value);
	    }
	};

	inline constexpr fill_fn fill;

Notes
		  Feature-test macro	       Value	Std		 Feature
	__cpp_lib_algorithm_default_value_type 202403  (C++26)	List-initializa-
     tion for
							      algorithms (1,2)

Example
     // Run this code

      #include <algorithm>
      #include <complex>
      #include <iostream>
      #include <vector>

      void println(const auto& seq)
      {
	  for (const auto& e : seq)
	      std::cout << e << ' ';
	  std::cout << '\n';
      }

      int main()
      {
	  std::vector<int> v{0, 1, 2, 3, 4, 5};

	  // set all elements to -1 using overload (1)
	  std::ranges::fill(v.begin(), v.end(), -1);
	  println(v);

	  // set all element to 10 using overload (2)
	  std::ranges::fill(v, 10);
	  println(v);

	  std::vector<std::complex<double>> nums{{1, 3}, {2, 2}, {4, 8}};
	  println(nums);
	  #ifdef __cpp_lib_algorithm_default_value_type
	      std::ranges::fill(nums, {4, 2}); // T gets deduced
	  #else
	      std::ranges::fill(nums, std::complex<double>{4, 2});
	  #endif
	  println(nums);
      }

Output:
      -1 -1 -1 -1 -1 -1
      10 10 10 10 10 10
      (1,3) (2,2) (4,8)
      (4,2) (4,2) (4,2)

See also
	ranges::fill_n		assigns a value to a number of elements
	(C++20) 		(niebloid)
	ranges::copy
	ranges::copy_if 	copies a range of elements to a new location
	(C++20) 		(niebloid)
	(C++20)
	ranges::generate	saves the result of a function in a range
	(C++20) 		(niebloid)
	ranges::transform	applies a function to a range of elements
	(C++20) 		(niebloid)
	ranges::generate_random fills a range with random numbers from a uniform
     random bit
	(C++26) 		generator
				(niebloid)
	fill			copy-assigns the given value to every element in
     a range
				(function template)

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