std::ranges::generate_random(3)

NAME
std::ranges::generate_random - std::ranges::generate_random

Synopsis
   Defined in header <random>
   Call signature
   template< class R, class G >
       requires ranges::output_range<R, std::invoke_result_t<G&>> && (since
                std::uniform_random_bit_generator<std::remove_cvref_t<G>> (1) C++26)
   constexpr ranges::borrowed_iterator_t<R>
       generate_random( R&& r, G&& g );
   template< class G, std::output_iterator<std::invoke_result_t<G&>> O,
             std::sentinel_for<O> S > (since
       requires std::uniform_random_bit_generator<std::remove_cvref_t<G>> (2) C++26)
   constexpr O
       generate_random( O first, S last, G&& g );
   template< class R, class G, class D >
       requires ranges::output_range<R, std::invoke_result_t<D&, G&>> &&
                std::invocable<D&, G&> && (3) (since
                std::uniform_random_bit_generator<std::remove_cvref_t<G>> C++26)
   constexpr ranges::borrowed_iterator_t<R>
       generate_random( R&& r, G&& g, D&& d );
   template< class G, class D,
   std::output_iterator<std::invoke_result_t<D&, G&>> O,
             std::sentinel_for<O> S > (since
       requires std::invocable<D&, G&> && (4) C++26)
                std::uniform_random_bit_generator<std::remove_cvref_t<G>>
   constexpr O
       generate_random( O first, S last, G&& g, D&& d );
   Attempts to generate random numbers with the generate_random member function of the
   random number generator or the distribution, which is expected to be more efficient.
   Falls back to element-wise generation if no generate_random member function is
   available.
   Let fallback operation be calling ranges::generate(std::forward<R>(r), std::ref(g))
   or ranges::generate(std::forward<R>(r), [&d, &g] { return std::invoke(d, g); }) for
   (1) or (3) respectively.
   1) Calls g.generate_random(std::forward<R>(r)) if this expression is well-formed.
   Otherwise, let I be std::invoke_result_t<G&>. If R models sized_range, fills r with
   ranges::size(r) values of I by performing an unspecified number of invocations of
   the form g() or g.generate_random(s), if such an expression is well-formed for a
   value N and an object s of type std::span<I, N>.
   Otherwise, performs the fallback operation.
   3) Calls d.generate_random(std::forward<R>(r), g) if this expression is well-formed.
   Otherwise, let I be std::invoke_result_t<D&, G&>. If R models sized_range, fills r
   with ranges::size(r) values of type I by performing an unspecified number of
   invocations of the form std::invoke(d, g) or d.generate_random(s, g), if such an
   expression is well-formed for a value N and an object s of type std::span<I, N>.
   Otherwise, performs the fallback operation.
   2,4) Equivalent to (1,3) respectively, where r is obtained from ranges::subrange<O,
   S>(std::move(first), last).
   If the effects of (1) or (3) are not equivalent to those of the corresponding
   fallback operation, the behavior is undefined.
   The value of N can differ between invocations. Implementations may select smaller
   values for shorter ranges.
   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 inhibited.
   In practice, they may be implemented as function objects, or with special compiler
   extensions.

Parameters
   first, last - iterator-sentinel pair that denotes the range to which random numbers
                 are written
   r - range to which random numbers are written
   g - uniform random bit generator
   d - random number distribution object

Notes
   At the time of the standardization of std::ranges::generate_random, there is no
   random number generator or distribution in the standard library that provides a
   generate_random member function.
   std::ranges::generate_random can be more efficient when used with a user-defined
   random number generator that wraps an underlying vectorized API.
          Feature-test macro Value Std Feature
   __cpp_lib_ranges_generate_random 202403L (C++26) std::ranges::generate_random

Example
// Run this code
 #include <algorithm>
 #include <iomanip>
 #include <iostream>
 #include <random>
 int main()
 {
     std::default_random_engine eng;
     std::default_random_engine::result_type rs[16]{};
     std::ranges::generate_random(rs, eng);
     std::cout << std::left;
     for (int i{}; auto n : rs)
         std::cout << std::setw(11) << n << (++i % 4 ? ' ' : '\n');
 }

Possible output:
 16807 282475249 1622650073 984943658
 1144108930 470211272 101027544 1457850878
 1458777923 2007237709 823564440 1115438165
 1784484492 74243042 114807987 1137522503

See also
   ranges::generate saves the result of a function in a range
   (C++20) (niebloid)
   uniform_random_bit_generator specifies that a type qualifies as a uniform random bit
   (C++20) generator
                        (concept)