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March 1, 2019 22:51
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variadic distribute
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| /// CC-0 2019, Florian Weber | |
| #include <cassert> | |
| #include <cstdint> | |
| #include <tuple> | |
| #include <type_traits> | |
| #include <utility> | |
| namespace impl { | |
| template <std::size_t Index, typename Value, typename... OutIt> | |
| void output(std::size_t i, Value& value, std::tuple<OutIt&...>& outputs) { | |
| if (i == Index) { | |
| auto& output = std::get<Index>(outputs); | |
| *output = std::move(value); | |
| ++output; | |
| } | |
| } | |
| template <typename InputIt, typename InputEnd, typename F, typename... OutIt, | |
| std::size_t... Indices> | |
| void distribute(InputIt it, InputEnd last, F fun, std::tuple<OutIt&...> outputs, | |
| std::index_sequence<Indices...>) { | |
| for (; it != last; ++it) { | |
| auto value = *it; | |
| const auto index = fun(std::as_const(value)); | |
| assert(index < sizeof...(Indices)); | |
| std::initializer_list{(output<Indices>(index, value, outputs), 0)...}; | |
| } | |
| } | |
| } // namespace impl | |
| template <typename InputIt, typename InputEnd, typename F, typename... OutIt> | |
| void distribute(InputIt first, InputEnd last, F fun, OutIt... outputs) { | |
| impl::distribute(first, last, fun, std::tie(outputs...), | |
| std::make_index_sequence<sizeof...(OutIt)>{}); | |
| } | |
| // And now for an example: | |
| #include <iostream> | |
| #include <iterator> | |
| #include <vector> | |
| int main() { | |
| auto v0 = std::vector<int>{}; | |
| auto v1 = std::vector<int>{}; | |
| auto v2 = std::vector<int>{}; | |
| const auto fun = [](int i) { return static_cast<unsigned>(((i % 3) + 3) % 3); }; | |
| distribute(std::istream_iterator<int>{std::cin}, std::istream_iterator<int>{}, fun, | |
| std::back_inserter(v0), std::back_inserter(v1), std::back_inserter(v2)); | |
| std::cout << "0 mod 3:\n"; | |
| std::copy(v0.begin(), v0.end(), std::ostream_iterator<int>{std::cout, ", "}); | |
| std::cout << "\n1 mod 3:\n"; | |
| std::copy(v1.begin(), v1.end(), std::ostream_iterator<int>{std::cout, ", "}); | |
| std::cout << "\n2 mod 3:\n"; | |
| std::copy(v2.begin(), v2.end(), std::ostream_iterator<int>{std::cout, ", "}); | |
| std::cout << '\n'; | |
| } |
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