std::ranges::sort(3)

NAME
std::ranges::sort - std::ranges::sort

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 = {} );
   Sorts the elements in the range [first, last) in non-descending order. The order of
   equivalent elements is not guaranteed to be preserved.
   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.
   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 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 - 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.

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

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

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
   (C++20) elements
                        (niebloid)
   ranges::partition divides a range of elements into two groups
   (C++20) (niebloid)
   sort sorts a range into ascending order
                        (function template)