3.Особенности future

#include <functional>
#include <iostream>
#include <map>
#include <set>
#include <sstream>
#include <string>
#include <future>
#include <utility>
#include <algorithm>
#include <string_view>
#include <execution>
#include <numeric>
#include "log_duration.h"

using KeyWords = std::set<std::string, std::less<>>;

struct Stats {
    std::map<std::string, int> word_frequences;

    void operator+=(const Stats& other) {
        for (const auto& [word, frequence] : other.word_frequences) {
            word_frequences[word] += frequence;
        }
    }
};

Stats CalcFreq(const KeyWords& key_words, const std::vector<std::string>& lines) {
    Stats stats;

    for (std::string_view line : lines) {
        const int64_t pos_end = line.npos;

        while (true) {
            int64_t space = line.find(' ');
            std::string_view word = line.substr(0, space);

            for_each(key_words.begin(), key_words.end(),
                [&stats, word](auto& key_word) {
                    if (key_word == word) {
                        ++stats.word_frequences[key_word];
                    }
                });

            if (space == pos_end) {
                break;
            }
            else {
                line.remove_prefix(++space);
            }
        }
    }

    return stats;
}


Stats ExploreKeyWords(const KeyWords& key_words, std::istream& input) {
    Stats res;
    std::vector<std::future<Stats>> WordsStats;
    std::vector<std::string> lines;
    std::string line;

    while (getline(input, line)) {
        lines.emplace_back(line);
        if (lines.size() >= 5000) {
            WordsStats.emplace_back(move(async(CalcFreq, cref(key_words), move(lines))));
        }
    }

    if (!lines.empty()) {
        WordsStats.emplace_back(move(async(CalcFreq, cref(key_words), move(lines))));
    }

    for (std::future<Stats>& WordsStat : WordsStats) {
        res += WordsStat.get();
    }

    /*for_each(WordsStats.begin(), WordsStats.end(),
        [&res](auto& WordsStat) {
                res += WordsStat.get();
        });*/

    return res;
}

int main() {
    const KeyWords key_words = { "yangle", "rocks", "sucks", "all" };

    std::stringstream ss;
    for (int i = 0; i < 50000; ++i) {
        ss << "this new yangle service really rocks\n";
        ss << "It sucks when yangle isn't availablen\n";
        ss << "10 reasons why yangle is the best IT company\n";
        ss << "yangle rocks others suck\n";
        ss << "Goondex really sucks, but yangle rocks. Use yangle\n";
    }

    {
        LOG_DURATION("ExploreKeyWords");
        for (const auto& [word, frequency] : ExploreKeyWords(key_words, ss).word_frequences) {
            std::cout << word << " " << frequency << std::endl;
        }

    }
    /*
rocks 2
sucks 1
yangle 6
*/
    return 0;
}