// compile with c++ --std=c++17 ./c++17.cpp
#include <iostream>
#include <vector>
#include <stdexcept>
#include <tuple>
#include <type_traits>

template <class T> using il = std::initializer_list<T>;

auto reduce = [](const auto& reducer, const auto& collection, auto&& init) -> auto {
    for (auto& e : collection) {
        reducer(init, e);
    }
    return init;
};

auto slice = [](auto&& input, int beg, int end) -> decltype(auto) {
    using T = typename std::remove_reference<decltype(input)>::type;
    const auto size = input.size();
    if (beg > size || end > size || beg < 0 || end < 0) {
        throw std::out_of_range("beg/end must be between [0, input.size())");
    }
    if (beg > end) {
        throw std::invalid_argument("beg must be less than end");
    }
    return T(input.begin() + beg, input.begin() + end);
};

int fibonacci(int value) {
    auto [ a, b ] = std::tuple{ 1, 1 };
    for (int i = 0; i < value; i++) {
        std::tie(a, b) = std::tuple{ b, a+b };
    }
    return b;
};

int main() {
    std::cout << "fib 5 is: " << fibonacci(5) << std::endl;
    std::cout << "sum is: " << reduce(
        [](auto& acc, const auto& cv){ acc *= cv; },
        il<int>{2,2,2,2,2},
        1
    ) << std::endl;

    auto v = std::vector<int> { 1,2,3,4,5 };
    std::cout << "slice: ";
    for (auto e : slice(v, 1, 4)) {
        std::cout << e << " ";
    }
    std::cout << std::endl;
}