std::ranges::sort(3)

💖 std::ranges::sort 💖

okay bestie, you're on the std::ranges::sort(3) page from the C++ Standard Libary manual, and yes it's literally the std::ranges::sort algorithm in all its C++20 glory. 🌈 This is the whole thing — every signature, parameter, code block, output line, note, and SEE ALSO reference is coming with us. No cap, nothing skipped. 💅

---

🎀 NAME 🎀

• std::ranges::sort — std::ranges::sort. That's the name. Iconic, honestly. 👑

---

✨ Synopsis ✨

Defined in header <algorithm>.

📜 Call signature 📜

          template< std::random_access_iterator I, std::sentinel_for<I> S,

                    class Comp = ranges::less, class Proj = std::identity >
          requires std::sortable<I, Comp, Proj>
       (1) (since C++20)
          constexpr I

              sort( I first, S last, Comp comp = {}, Proj proj = {} );
          template< ranges::random_access_range R, class Comp =
          ranges::less,

                    class Proj = std::identity >
       (2) (since C++20)
          requires std::sortable<ranges::iterator_t<R>, Comp, Proj>
          constexpr ranges::borrowed_iterator_t<R>

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

So what does it do? It sorts the elements in the range [first, last) in non-descending order. The order of equivalent elements is not guaranteed to be preserved. That's the tea. 🫖

A sequence is sorted with respect to a comparator comp if for any iterator it pointing to the sequence and any non-negative integer n such that it + n is a valid iterator pointing to an element of the sequence, std::invoke(comp, std::invoke(proj, *(it + n)), std::invoke(proj, *it)) evaluates to false. Yes, that's the official vibe check. 😌

1. Elements are compared using the given binary comparison function comp.
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 — iterator-sentinel defining the range to sort.
• r — the range to sort.
• comp — comparison to apply to the projected elements.
• proj — projection to apply to the elements.

---

🦋 Return value 🦋

An iterator equal to last. That's it. Slay. 💅

---

🔥 Complexity 🔥

\(\scriptsize \mathcal{O}(N\cdot\log{(N)})\)𝓞(N·log(N)) comparisons and projections, where N = ranges::distance(first, last). Math girlies rise. 🧮✨

---

👑 Possible implementation 👑

Note that typical implementations use Introsort. See also the implementation in MSVC STL and libstdc++.

Here's the implementation exactly as the page gives it — no edits, just handing it over:

       struct sort_fn {
           template<std::random_access_iterator I, std::sentinel_for<I> S,
                    class Comp = ranges::less, class Proj = std::identity>
           requires std::sortable<I, Comp, Proj>
           constexpr I
               operator()(I first, S last, Comp comp = {}, Proj proj = {})
       const
           {
               if (first == last)
                   return first;

               I last_iter = ranges::next(first, last);
               ranges::make_heap(first, last_iter, std::ref(comp),
       std::ref(proj));
               ranges::sort_heap(first, last_iter, std::ref(comp),
       std::ref(proj));

               return last_iter;
           }

           template<ranges::random_access_range R, class Comp = ranges::less,
                    class Proj = std::identity>
           requires std::sortable<ranges::iterator_t<R>, Comp, Proj>
           constexpr ranges::borrowed_iterator_t<R>
               operator()(R&& r, Comp comp = {}, Proj proj = {}) const
           {
               return (*this)(ranges::begin(r), ranges::end(r),
       std::move(comp), std::move(proj));
           } };

       inline constexpr sort_fn sort {};

---

💜 Notes 💜

std::sort uses std::iter_swap to swap elements, whereas ranges::sort instead uses ranges::iter_swap (which performs ADL for iter_swap, unlike std::iter_swap). Little swap lore for you. 🫶

---

🍓 Example 🍓

// Run this code

        #include <algorithm>
        #include <array>
        #include <functional>
        #include <iomanip>
        #include <iostream>

        void print(auto comment, auto const& seq, char term = ' ')
        {
            for (std::cout << comment << '\n'; auto const& elem : seq)
                std::cout << elem << term;
            std::cout << '\n';
        }

        struct Particle
        {
            std::string name; double mass; // MeV
            template<class Os> friend
            Os& operator<<(Os& os, Particle const& p)
            {
                return os << std::left << std::setw(8) << p.name << " : " <<
       p.mass << ' ';
            }
        };

        int main()
        {
            std::array s {5, 7, 4, 2, 8, 6, 1, 9, 0, 3};

            namespace ranges = std::ranges;

            ranges::sort(s);
            print("Sort using the default operator<", s);

            ranges::sort(s, ranges::greater());
            print("Sort using a standard library compare function object", s);

            struct
            {
                bool operator()(int a, int b) const { return a < b; }
            } customLess;
            ranges::sort(s.begin(), s.end(), customLess);
            print("Sort using a custom function object", s);

            ranges::sort(s, [](int a, int b) { return a > b; });
            print("Sort using a lambda expression", s);

            Particle particles[]
            {
                {"Electron", 0.511}, {"Muon", 105.66}, {"Tau", 1776.86},
                {"Positron", 0.511}, {"Proton", 938.27}, {"Neutron", 939.57}
            };
            ranges::sort(particles, {}, &Particle::name);
            print("\nSort by name using a projection", particles, '\n');
            ranges::sort(particles, {}, &Particle::mass);
            print("Sort by mass using a projection", particles, '\n');
        }

🖨️ Output 🖨️

        Sort using the default operator<
        0 1 2 3 4 5 6 7 8 9
        Sort using a standard library compare function object
        9 8 7 6 5 4 3 2 1 0
        Sort using a custom function object
        0 1 2 3 4 5 6 7 8 9
        Sort using a lambda expression
        9 8 7 6 5 4 3 2 1 0

        Sort by name using a projection
        Electron : 0.511
        Muon     : 105.66
        Neutron  : 939.57
        Positron : 0.511
        Proton   : 938.27
        Tau      : 1776.86

        Sort by mass using a projection
        Electron : 0.511
        Positron : 0.511
        Muon     : 105.66
        Proton   : 938.27
        Neutron  : 939.57
        Tau      : 1776.86

---

🌈 See also 🌈

• ranges::partial_sort — sorts the first N elements of a range (C++20) (niebloid).
• ranges::stable_sort — sorts a range of elements while preserving order between equal elements (C++20) (niebloid).
• ranges::partition — divides a range of elements into two groups (C++20) (niebloid).
• sort — sorts a range into ascending order (function template).

---

that's the page, bestie! 💅 source: http://cppreference.com • version/date: 2024.06.10 • page: std::ranges::sort(3) ✨