std::ranges...ment_result(3)

💖 NAME 💖

std::ranges::minmax_element,std::ranges::minmax_element_result

okay so this page is from the C++ Standard Library manual — and yes, the header literally says “C++ Standard Libary”, we are not fixing it, it’s iconic. It’s all about the std::ranges::minmax_element and std::ranges::minmax_element_result duo. it’s giving algorithm bestie energy: smallest and largest, handled. no cap 🎀

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✨ Synopsis ✨

okay so the synopsis is a little cursed with line wrapping, but here’s the exact thing, every token intact:

          Defined in header <algorithm>
          Call signature
          template< std::forward_iterator I, std::sentinel_for<I> S, class Proj
       =
          std::identity,

                    std::indirect_strict_weak_order<std::projected<I, Proj>>
       Comp  (1) (since
          = ranges::less >
       C++20)
          constexpr minmax_element_result<I>

              minmax_element( I first, S last, Comp comp = {}, Proj proj = {}
       );
          template< ranges::forward_range R, class Proj = std::identity,

                    std::indirect_strict_weak_order<
                        std::projected<ranges::iterator_t<R>, Proj>> Comp =
       (2) (since
          ranges::less >
       C++20)
          constexpr minmax_element_result<ranges::borrowed_iterator_t<R>>

              minmax_element( R&& r, Comp comp = {}, Proj proj = {} );

Helper types
          template< class I >
       (3) (since
          using minmax_element_result = ranges::min_max_result<I>;
       C++20)

1. Finds the smallest and largest 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 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. iykyk, niebloid life 💅

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🌸 Parameters 🌸

• first, last — the iterator-sentinel pair that marks the range you’re examining. literally the start/end-ish combo for the range to examine.
• r — the range to examine. same energy, but as a whole range object.
• comp — the comparison you want applied to the projected elements.
• proj — the projection you want applied to the elements.

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👑 Return value 👑

You get an object with two iterators inside: the first one points at the smallest element, and the second one points at the greatest element. If the range is empty, you get {first, first}. If several elements are equivalent to the smallest element, you get the iterator to the first such element. If several elements are equivalent to the largest element, you get the iterator to the last such element. periodt 🫶

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🔥 Complexity 🔥

At most std::max(std::floor(1.5 * (N − 1)), 0.0) applications of the comparison, and twice as many applications of the projection, where N = ranges::distance(first, last). that’s the whole budget, bestie. no extra 💀

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🧚 Possible implementation 🧚

here’s the possible implementation, copied exactly because we do not mess with code:

       struct minmax_element_fn {
           template<std::forward_iterator I, std::sentinel_for<I> S, class Proj
       = std::identity,
                    std::indirect_strict_weak_order<std::projected<I, Proj>>
       Comp = ranges::less>
           constexpr ranges::minmax_element_result<I>
               operator()(I first, S last, Comp comp = {}, Proj proj = {})
       const
           {
               auto min = first, max = first;

               if (first == last || ++first == last)
                   return {min, max};

               if (std::invoke(comp, std::invoke(proj, *first),
                                     std::invoke(proj, *min)))
                   min = first;
               else
                   max = first;

               while (++first != last)
               {
                   auto i = first;
                   if (++first == last)
                   {
                       if (std::invoke(comp, std::invoke(proj, *i),
                                             std::invoke(proj, *min)))
                           min = i;
                       else if (!(std::invoke(comp, std::invoke(proj, *i),
                                                    std::invoke(proj, *max))))
                           max = i;
                       break;
                   }
                   else
                   {
                       if (std::invoke(comp, std::invoke(proj, *first),
                                             std::invoke(proj, *i)))
                       {
                         if (std::invoke(comp, std::invoke(proj, *first),
                                               std::invoke(proj, *min)))
                             min = first;
                         if (!(std::invoke(comp, std::invoke(proj, *i),
                                                 std::invoke(proj, *max))))
                             max = i;
                       }
                       else
                       {
                           if (std::invoke(comp, std::invoke(proj, *i),
                                                 std::invoke(proj, *min)))
                               min = i;
                           if (!(std::invoke(comp, std::invoke(proj, *first),
                                                   std::invoke(proj, *max))))
                               max = first;
                       }
                   }
               }
               return {min, max};
           }

           template<ranges::forward_range R, class Proj = std::identity,
                    std::indirect_strict_weak_order<
                        std::projected<ranges::iterator_t<R>, Proj>> Comp =
       ranges::less>
           constexpr
       ranges::minmax_element_result<ranges::borrowed_iterator_t<R>>
               operator()(R&& r, Comp comp = {}, Proj proj = {}) const
           {
               return (*this)(ranges::begin(r), ranges::end(r), std::ref(comp),
       std::ref(proj));
           } };

       inline constexpr minmax_element_fn minmax_element;

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🌈 Example 🌈

        #include <algorithm>
        #include <iostream>
        #include <iterator>
        namespace ranges = std::ranges;

        int main()
        {
            const auto v = {3, 9, 1, 4, 1, 2, 5, 9};
            const auto [min, max] = ranges::minmax_element(v);
            std::cout
                << "min = " << *min << ", at [" << ranges::distance(v.begin(),
       min) << "]\n"
                << "max = " << *max << ", at [" << ranges::distance(v.begin(),
       max) << "]\n";
        }

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🍓 Output 🍓

        min = 1, at [2]
        max = 9, at [7]

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👀 See also 👀

• ranges::min_element — returns the smallest element in a range. (C++20) (niebloid)
• ranges::max_element — returns the largest element in a range. (C++20) (niebloid)
• ranges::minmax — returns the smaller and larger of two elements. (C++20) (niebloid)
• minmax_element — returns the smallest and the largest elements in a range. (C++11) (function template)

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source: cppreference.com · date: 2024.06.10 · page: std::ranges...ment_result(3) — mwah, go slay some ranges bestie 💖✨