Python-like functional functions implemented in C++

join.hpp

#include <sstream>

template <class _StrTyp, class _SeqTyp, class... _Arg>
_StrTyp join(_StrTyp&& seperator, _SeqTyp&& sequence, _Arg&&... args)
{
    using _Elem = typename _StrTyp::value_type;
    using _Traits = typename _StrTyp::traits_type;
    using _Alloc = typename _StrTyp::allocator_type;
    std::basic_stringstream<_Elem, _Traits, _Alloc> oss;
    ((oss << args), ...);
    auto it = std::begin(sequence);
    oss << *it++;
    while (it != std::end(sequence))
        oss << seperator << *it++;
    return oss.str();
}


#include <iostream>

int main()
{
    std::cout << join(
        std::string{ "-" }, std::vector<int>{101, 202, 303, 404},
        std::showbase, std::hex
    ) << std::endl;
}

mapset.hpp

#include <vector>
#include <iterator>
#include <algorithm>
#include <functional>

template <class _Map>
std::vector<typename _Map::key_type> keyset(const _Map& map)
{
    std::vector<typename _Map::key_type> result;
    result.reserve(map.size());
    std::transform(map.cbegin(), map.cend(), std::back_inserter(result), [](typename _Map::const_reference kvpair) {
        return kvpair.first;
    });
    return result;
}

template <class _Map>
std::vector<typename _Map::mapped_type> valueset(const _Map& map)
{
    std::vector<typename _Map::mapped_type> result;
    result.reserve(map.size());
    std::transform(map.cbegin(), map.cend(), std::back_inserter(result), [](typename _Map::const_reference kvpair) {
        return kvpair.second;
    });
    return result;
}

template <class _Map>
std::vector<std::reference_wrapper<typename _Map::mapped_type>> valueset(_Map& map)
{
    std::vector<std::reference_wrapper<typename _Map::mapped_type>> result;
    result.reserve(map.size());
    std::transform(map.begin(), map.end(), std::back_inserter(result), [](typename _Map::reference kvpair) {
        return std::ref(kvpair.second);
    });
    return result;
}


#include <iostream>

int main()
{
    std::map<int, double> map{
        {1, 9.0},
        {2, 9.9},
        {3, 9.99},
        {4, 9.999},
    };
    auto ks = keyset(map);
    auto vs = valueset(map);
    for (auto& k : ks) std::cout << k << '\n';
    std::cout << "------------------\n";
    for (auto& v : vs) std::cout << v << '\n';
    for (auto& v : vs) v += 100.0;
    std::cout << "------------------\n";
    for (auto& v : vs) std::cout << v << '\n';
    std::cout << "------------------\n";
    for (auto& [k, v] : map) std::cout << v << '\n';

    return 0;
}