std::ranges::search_n

#include <algorithm>
#include <cassert>
#include <complex>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
int main()
{
    namespace ranges = std::ranges;
    static constexpr auto nums = {1, 2, 2, 3, 4, 1, 2, 2, 2, 1};
    constexpr int count{3};
    constexpr int value{2};
    typedef int count_t, value_t;
    constexpr auto result1 = ranges::search_n
    (
        nums.begin(), nums.end(), count, value
    );
    static_assert // найдено
    (
        result1.size() == count &&
        std::distance(nums.begin(), result1.begin()) == 6 &&
        std::distance(nums.begin(), result1.end()) == 9
    );
    constexpr auto result2 = ranges::search_n(nums, count, value);
    static_assert // найдено
    (
        result2.size() == count &&
        std::distance(nums.begin(), result2.begin()) == 6 &&
        std::distance(nums.begin(), result2.end()) == 9
    );
    constexpr auto result3 = ranges::search_n(nums, count, value_t{5});
    static_assert // не найдено
    (
        result3.size() == 0 &&
        result3.begin() == result3.end() &&
        result3.end() == nums.end()
    );
    constexpr auto result4 = ranges::search_n(nums, count_t{0}, value_t{1});
    static_assert // не найдено
    (
        result4.size() == 0 &&
        result4.begin() == result4.end() &&
        result4.end() == nums.begin()
    );
    constexpr char symbol{'B'};
    auto to_ascii = [](const int z) -> char { return 'A' + z - 1; };
    auto is_equ = [](const char x, const char y) { return x == y; };
    std::cout << "Найти подпоследовательность " << std::string(count, symbol) << " в ";
    std::ranges::transform(nums, std::ostream_iterator<char>(std::cout, ""), to_ascii);
    std::cout << '\n';
    auto result5 = ranges::search_n(nums, count, symbol, is_equ, to_ascii);
    if (not result5.empty())
        std::cout << "Найдено в позиции "
                  << ranges::distance(nums.begin(), result5.begin()) << '\n';
    std::vector<std::complex<double>> nums2{{4, 2}, {4, 2}, {1, 3}};
    #ifdef __cpp_lib_algorithm_default_value_type
        auto it = ranges::search_n(nums2, 2, {4, 2});
    #else
        auto it = ranges::search_n(nums2, 2, std::complex<double>{4, 2});
    #endif
    assert(it.size() == 2);
}