std::ranges::in_out_out_result(3)

NAME
std::ranges::in_out_out_result - std::ranges::in_out_out_result

Synopsis
   Defined in header <algorithm>
   template< class I, class O1, class O2 > (since C++20)
   struct in_out_out_result;
   ranges::in_out_out_result is a class template that provides a way to store three
   iterators as a single unit.
   This class template has no base classes or declared members other than those shown
   below. Thus it is suitable for use with structured bindings.
   All special member functions of this class template are implicitly declared, which
   makes specializations be aggregate classes, and propagate triviality,
   potentially-throwing-ness, and constexpr-ness of corresponding operations on data
   members.

Template parameters
   I, O1, O2 - the types of the objects that the ranges::in_out_out_result stores.
   Data members
   Member name Definition
   in a value (that is supposed to be an iterator) of type I.
               (public member object)
   out1 a value (that is supposed to be an iterator) of type O1.
               (public member object)
   out2 a value (that is supposed to be an iterator) of type O2.
               (public member object)
   All these members are declared with [[no_unique_address]] attribute.

Member functions
std::ranges::in_out_out_result::operator in_out_out_result<II, OO1, OO2>
   template<class II, class OO1, class OO2>
   requires std::convertible_to<const I&, II> &&
            std::convertible_to<const O1&, OO1> && (1)
            std::convertible_to<const O2&, OO2>
   constexpr operator in_out_out_result<II, OO1, OO2>() const &;
   template<class II, class OO1, class OO2>
   requires std::convertible_to<I, II> &&
            std::convertible_to<O1, OO1> && (2)
            std::convertible_to<O2, OO2>
   constexpr operator in_out_out_result<II, OO1, OO2>() &&;
   Converts *this to the result by constructing every data member of the result from
   the corresponding member of *this.
   1) Equivalent to return {in, out1, out2};.
   2) Equivalent to return {std::move(in), std::move(out1), std::move(out2)};.

Standard library
   The following standard library functions use ranges::in_out_out_result as the return
   type:
         Algorithm functions
   ranges::partition_copy copies a range dividing the elements into two groups
   (C++20) (niebloid)

Synopsis
 namespace std::ranges
 {
     template<class I, class O1, class O2>
     struct in_out_out_result
     {
         [[no_unique_address]] I in;
         [[no_unique_address]] O1 out1;
         [[no_unique_address]] O2 out2;
         template<class II, class OO1, class OO2>
         requires std::convertible_to<const I&, II> &&
                  std::convertible_to<const O1&, OO1> &&
                  std::convertible_to<const O2&, OO2>
         constexpr operator in_out_out_result<II, OO1, OO2>() const &
         {
             return {in, out1, out2};
         }
         template<class II, class OO1, class OO2>
         requires std::convertible_to<I, II> &&
                  std::convertible_to<O1, OO1> &&
                  std::convertible_to<O2, OO2>
         constexpr operator in_out_out_result<II, OO1, OO2>() &&
         {
             return {std::move(in), std::move(out1), std::move(out2)};
         }
     };
 }

Notes
   Each standard library algorithm that uses this family of return types declares a new
   alias type, e.g. using merge_result = in_in_out_result<I1, I2, O>;.
   The names for such aliases are formed by adding the suffix "_result" to the
   algorithm's name. So, the return type of std::ranges::merge can be named as
   std::ranges::merge_result.
   Unlike std::pair and std::tuple, this class template has data members of meaningful
   names.

Example
// Run this code
 #include <algorithm>
 #include <array>
 #include <cctype>
 #include <iostream>
 #include <iterator>
 #include <ranges>
 #include <string_view>
 void print(std::string_view rem, auto first, auto last)
 {
     for (std::cout << rem << ": { "; first != last; ++first)
         std::cout << *first << ' ';
     std::cout << "}\n";
 }
 int main()
 {
     constexpr std::string_view in {"TvEeNcStOoRr"};
     std::array<char, in.size()> o1, o2;
     const auto result = std::ranges::partition_copy(in, o1.begin(), o2.begin(),
         [](char c) { return std::isupper(c); });
     print("in", in.begin(), result.in);
     print("o1", o1.begin(), result.out1);
     print("o2", o2.begin(), result.out2);
 }

Output:
 in: { T v E e N c S t O o R r }
 o1: { T E N S O R }
 o2: { v e c t o r }

See also
   pair implements binary tuple, i.e. a pair of values
           (class template)
   tuple implements fixed size container, which holds elements of possibly different
   (C++11) types
           (class template)