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

NAME
     std::ranges::generate - std::ranges::generate

Synopsis
	Defined in header <algorithm>
	Call signature
	template< std::input_or_output_iterator O, std::sentinel_for<O> S,

		  std::copy_constructible F >
	requires  std::invocable<F&>  && std::indirectly_writable<O,	     (1)
     (since C++20)
	std::invoke_result_t<F&>>
	constexpr O

	    generate( O first, S last, F gen );
	template< class R, std::copy_constructible F >

	requires std::invocable<F&> && ranges::output_range<R,
	std::invoke_result_t<F&>>					     (2)
     (since C++20)
	constexpr ranges::borrowed_iterator_t<R>

	    generate( R&& r, F gen );

	1)  Assigns  the result of successive invocations of the function object
     gen to each
	element in the range [first, last).
	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 modify
	r	    - the range of elements to modify
	gen	    - the generator function object

Return value
	An output iterator that compares equal to last.

Complexity
	Exactly  ranges::distance(first,  last) invocations of gen() and assign-
     ments.

Possible implementation
       struct generate_fn
       {
	   template<std::input_or_output_iterator O, std::sentinel_for<O> S,
		    std::copy_constructible F>
	   requires std::invocable<F&> &&  std::indirectly_writable<O,	std::in-
     voke_result_t<F&>>
	   constexpr O operator()(O first, S last, F gen) const
	   {
	       for (; first != last; *first = std::invoke(gen), ++first)
	       {}
	       return first;
	   }

	   template<class R, std::copy_constructible F>
	   requires   std::invocable<F&>   &&  ranges::output_range<R,	std::in-
     voke_result_t<F&>>
	   constexpr ranges::borrowed_iterator_t<R>  operator()(R&&  r,  F  gen)
     const
	   {
	       return (*this)(ranges::begin(r), ranges::end(r), std::move(gen));
	   }
       };

       inline constexpr generate_fn generate {};

Example
     // Run this code

      #include <algorithm>
      #include <array>
      #include <iostream>
      #include <random>
      #include <string_view>

      auto dice()
      {
	  static std::uniform_int_distribution<int> distr {1, 6};
	  static std::random_device device;
	  static std::mt19937 engine {device()};
	  return distr(engine);
      }

      void iota(auto& v, int n)
      {
	  std::ranges::generate(v, [&n]() mutable { return n++; });
      }

      void print(std::string_view comment, const auto& v)
      {
	  for (std::cout << comment; int i : v)
	      std::cout << i << ' ';
	  std::cout << '\n';
      }

      int main()
      {
	  std::array<int, 8> v;

	  std::ranges::generate(v.begin(), v.end(), dice);
	  print("dice: ", v);
	  std::ranges::generate(v, dice);
	  print("dice: ", v);

	  iota(v, 1);
	  print("iota: ", v);
      }

Possible output:
      dice: 4 3 1 6 6 4 5 5
      dice: 4 2 5 3 6 2 6 2
      iota: 1 2 3 4 5 6 7 8

See also
	ranges::generate_n	saves the result of N applications of a function
	(C++20) 		(niebloid)
	ranges::fill		assigns a range of elements a certain value
	(C++20) 		(niebloid)
	ranges::fill_n		assigns a value to a number of elements
	(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)
				assigns the results of successive function calls
     to every
	generate		element in a range
				(function template)

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