std::ranges::min_element(3)

NAME
std::ranges::min_element - std::ranges::min_element

Synopsis
   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 I
       min_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 ranges::borrowed_iterator_t<R>
       min_element( R&& r, Comp comp = {}, Proj proj = {} );
   1) Finds the smallest element 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.

Parameters
   first, last - iterator-sentinel pair denoting the range to examine
   r - the range to examine
   comp - comparison to apply to the projected elements
   proj - projection to apply to the elements

Return value
   Iterator to the smallest element in the range [first, last). If several elements in
   the range are equivalent to the smallest element, returns the iterator to the first
   such element. Returns last if the range is empty (i.e., first == last).

Complexity
   Exactly max(N - 1, 0) comparisons, where N = ranges::distance(first, last).

Possible implementation
struct min_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 I operator()(I first, S last, Comp comp = {}, Proj proj = {}) const
    {
        if (first == last)
            return last;
        auto smallest = first;
        while (++first != last)
            if (std::invoke(comp, std::invoke(proj, *first), std::invoke(proj, *smallest)))
                smallest = first;
        return smallest;
    }
    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::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 min_element_fn min_element;

Example
// Run this code
 #include <algorithm>
 #include <array>
 #include <cmath>
 #include <iostream>
 int main()
 {
     namespace ranges = std::ranges;
     std::array v{3, 1, -13, 1, 3, 7, -13};
     auto iterator = ranges::min_element(v.begin(), v.end());
     auto position = ranges::distance(v.begin(), iterator);
     std::cout << "min element is v[" << position << "] == " << *iterator << '\n';
     auto abs_compare = [](int a, int b) { return (std::abs(a) < std::abs(b)); };
     iterator = ranges::min_element(v, abs_compare);
     position = ranges::distance(v.begin(), iterator);
     std::cout << "|min| element is v[" << position << "] == " << *iterator << '\n';
 }

Output:
 min element is v[2] == -13
 |min| element is v[1] == 1

See also
   ranges::max_element returns the largest element in a range
   (C++20) (niebloid)
   ranges::minmax_element returns the smallest and the largest elements in a range
   (C++20) (niebloid)
   ranges::max returns the greater of the given values
   (C++20) (niebloid)
   min_element returns the smallest element in a range
                        (function template)