atomic

#include <algorithm>
#include <iostream>
#include <numeric>
#include <random>
#include <string>
#include <string_view>
#include <vector>
#include <execution>

#include "log_duration.h"

using namespace std;

string GenerateWord(mt19937& generator, int max_length) {
    const int length = uniform_int_distribution(1, max_length)(generator);
    string word;
    word.reserve(length);
    for (int i = 0; i < length; ++i) {
        word.push_back(uniform_int_distribution('a', 'z')(generator));
    }
    return word;
}

template <template <typename> typename Container>
Container<string> GenerateDictionary(mt19937& generator, int word_count, int max_length) {
    vector<string> words;
    words.reserve(word_count);
    for (int i = 0; i < word_count; ++i) {
        words.push_back(GenerateWord(generator, max_length));
    }
    return Container(words.begin(), words.end());
}

template <typename Strings, typename Predicate, typename Function>
void Test(string_view mark, const Strings& strings, Predicate predicate, Function function) {
    LOG_DURATION(mark);
    const auto result = function(strings, predicate);
    cout << result.size() << " " << result[5].substr(0, 5) << endl;
}

#define TEST(function) \
    Test(#function, strings, predicate, function<vector<string>, decltype(predicate)>)

template <typename Container, typename Predicate, typename Type = typename Container::value_type>
vector<Type> CopyIfUnordered(const Container& container, Predicate predicate) {
    vector<Type> result;
    result.reserve(container.size());
    // atomic_int size = -1;
    atomic<Type*> destination;

for_each(execution::par, container.begin(), container.end(),
                    [&predicate, &result, &destination](const Type& item) {
                        if (predicate(item)) {
                            destination = &result.emplace_back();
                            *destination = item;
                            // size.fetch_add(1);
                            // result[size] = item;
                        }
                    });
    return result;
}

int main() {
    vector<int> numbers(1'000);
    iota(numbers.begin(), numbers.end(), 0);

    const vector<int> even_numbers = CopyIfUnordered(numbers, [](int number) {
        return number % 2 == 0;
    });
    for (const int number : even_numbers) {
        cout << number << " "s;
    }
    cout << endl;
    // выведет все чётные числа от 0 до 999

    mt19937 generator;

    const auto strings = GenerateDictionary<vector>(generator, 50'000, 3000);
    auto predicate = [](const string& s) {
        return count(s.begin(), s.end(), 'a') < 100;
    };

    TEST(CopyIfUnordered);
}