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 > (1) (since C++20)
   constexpr O fill( O first, S last, const T& value );
   template< class T, ranges::output_range<const T&> R >
   constexpr ranges::borrowed_iterator_t<R> fill( R&& r, const T& (2) (since C++20)
   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::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 may not be specified when calling any of them.
     * None of them is visible to argument-dependent lookup.
     * When one of them is found by normal unqualified lookup for the name to the left
       of the function-call operator, it inhibits argument-dependent lookup.
   In practice, they may be implemented as function objects, or with special 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 T, std::output_iterator<const T&> O, std::sentinel_for<O> S >
     constexpr O operator()( O first, S last, const T& value ) const
     {
         while (first != last) {
             *first++ = value;
         }
         return first;
     }
     template< class T, ranges::output_range<const T&> R >
     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;

Example
   The following code uses ranges::fill() to set all of the elements of a vector of
   ints first to -1, then to 10. // Run this code
 #include <algorithm>
 #include <vector>
 #include <iostream>
 int main()
 {
     std::vector<int> v{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
     namespace ranges = std::ranges;
     ranges::fill(v.begin(), v.end(), -1);
     for (auto elem : v) {
         std::cout << elem << " ";
     }
     std::cout << "\n";
     ranges::fill(v, 10);
     for (auto elem : v) {
         std::cout << elem << " ";
     }
     std::cout << "\n";
 }

Output:
 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
 10 10 10 10 10 10 10 10 10 10

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)
   fill copy-assigns the given value to every element in a range
                     (function template)