std::ranges::partition_copy,std::ranges::partition_copy_result(3)

NAME
std::ranges::partition_copy,std::ranges::partition_copy_result - std::ranges::partition_copy,std::ranges::partition_copy_result

Synopsis
   Defined in header <algorithm>
   Call signature
   template< std::input_iterator I, std::sentinel_for<I> S,
             std::weakly_incrementable O1, std::weakly_incrementable O2,
             class Proj = std::identity,
             std::indirect_unary_predicate<std::projected<I, Proj>> Pred > (since
   requires std::indirectly_copyable<I, O1> && (1) C++20)
            std::indirectly_copyable<I, O2>
   constexpr partition_copy_result<I, O1, O2>
       partition_copy( I first, S last, O1 out_true, O2 out_false,
                       Pred pred, Proj proj = {} );
   template< ranges::input_range R,
             std::weakly_incrementable O1, std::weakly_incrementable O2,
             class Proj = std::identity,
             std::indirect_unary_predicate<std::projected<iterator_t<R>,
   Proj>> Pred > (2) (since
   requires std::indirectly_copyable<ranges::iterator_t<R>, O1> && C++20)
            std::indirectly_copyable<ranges::iterator_t<R>, O2>
   constexpr partition_copy_result<ranges::borrowed_iterator_t<R>, O1, O2>
       partition_copy( R&& r, O1 out_true, O2 out_false,
                       Pred pred, Proj proj = {} );

Helper types
   template< class I, class O1, class O2 > (3) (since
   using partition_copy_result = ranges::in_out_out_result<I, O1, O2>; C++20)
   1) Copies the elements from the input range [first, last) to two different output
   ranges depending on the value returned by the predicate pred. The elements that
   satisfy the predicate pred after projection by proj are copied to the range
   beginning at out_true. The rest of the elements are copied to the range beginning at
   out_false. The behavior is undefined if the input range overlaps either of the
   output ranges.
   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 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 - the input range of elements to copy from
   r - the input range of elements to copy from
   out_true - the beginning of the output range for the elements that satisfy pred
   out_false - the beginning of the output range for the elements that do not satisfy
                 pred
   pred - predicate to apply to the projected elements
   proj - projection to apply to the elements

Return value
   {last, o1, o2}, where o1 and o2 are the ends of the output ranges respectively,
   after the copying is complete.

Complexity
   Exactly ranges::distance(first, last) applications of the corresponding predicate
   comp and any projection proj.

Possible implementation
   struct partition_copy_fn
   {
       template<std::input_iterator I, std::sentinel_for<I> S,
                std::weakly_incrementable O1, std::weakly_incrementable O2,
                class Proj = std::identity, std::indirect_unary_predicate<
                std::projected<I, Proj>> Pred>
       requires std::indirectly_copyable<I, O1> && std::indirectly_copyable<I, O2>
       constexpr ranges::partition_copy_result<I, O1, O2>
           operator()(I first, S last, O1 out_true, O2 out_false,
                      Pred pred, Proj proj = {}) const
       {
           for (; first != last; ++first)
               if (!!std::invoke(pred, std::invoke(proj, *first)))
                   *out_true = *first, ++out_true;
               else
                   *out_false = *first, ++out_false;
           return {std::move(first), std::move(out_true), std::move(out_false)};
       }
       template<ranges::input_range R,
                std::weakly_incrementable O1, std::weakly_incrementable O2,
                class Proj = std::identity,
                std::indirect_unary_predicate<std::projected<iterator_t<R>, Proj>> Pred>
       requires std::indirectly_copyable<ranges::iterator_t<R>, O1> &&
                std::indirectly_copyable<ranges::iterator_t<R>, O2>
       constexpr ranges::partition_copy_result<ranges::borrowed_iterator_t<R>, O1, O2>
           operator()(R&& r, O1 out_true, O2 out_false, Pred pred, Proj proj = {}) const
       {
           return (*this)(ranges::begin(r), ranges::end(r), std::move(out_true),
                        std::move(out_false), std::move(pred), std::move(proj));
       }
   };
   inline constexpr partition_copy_fn partition_copy {};

Example
// Run this code
 #include <algorithm>
 #include <cctype>
 #include <iostream>
 #include <iterator>
 #include <vector>
 int main()
 {
     const auto in = {'N', '3', 'U', 'M', '1', 'B', '4', 'E', '1', '5', 'R', '9'};
     std::vector<int> o1(size(in)), o2(size(in));
     auto pred = [](char c) { return std::isalpha(c); };
     auto ret = std::ranges::partition_copy(in, o1.begin(), o2.begin(), pred);
     std::ostream_iterator<char> cout {std::cout, " "};
     std::cout << "in = ";
     std::ranges::copy(in, cout);
     std::cout << "\no1 = ";
     std::copy(o1.begin(), ret.out1, cout);
     std::cout << "\no2 = ";
     std::copy(o2.begin(), ret.out2, cout);
     std::cout << '\n';
 }

Output:
 in = N 3 U M 1 B 4 E 1 5 R 9
 o1 = N U M B E R
 o2 = 3 1 4 1 5 9

See also
   ranges::partition divides a range of elements into two groups
   (C++20) (niebloid)
   ranges::stable_partition divides elements into two groups while preserving their
   (C++20) relative order
                        (niebloid)
   ranges::copy
   ranges::copy_if copies a range of elements to a new location
   (C++20) (niebloid)
   (C++20)
   ranges::remove_copy copies a range of elements omitting those that satisfy
   ranges::remove_copy_if specific criteria
   (C++20) (niebloid)
   (C++20)
   partition_copy copies a range dividing the elements into two groups
   (C++11) (function template)