1 | #include <tuple>
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2 | #include <utility>
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3 | #include <iostream>
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4 | #include <cstddef>
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5 |
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6 | enum class color { red, blue, black };
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7 |
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8 | class Geo {
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9 | public:
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10 | virtual void draw () const = 0;
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11 | };
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12 |
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13 | class Circle : public Geo {
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14 | public:
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15 | struct Data {
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16 | int x, y, r;
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17 | color fgcolor, bgcolor;
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18 | } data;
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19 | constexpr Circle (const Data& data) : data(data) {}
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20 |
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21 | virtual void draw () const override;
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22 | };
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23 |
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24 | class Rectangle : public Geo {
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25 | public:
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26 | struct Data {
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27 | int x, y, w, h;
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28 | color fgcolor;
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29 | } data;
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30 | constexpr Rectangle (const Data& data) : data(data) {}
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31 |
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32 | virtual void draw () const override;
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33 | };
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34 |
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35 | class Textfield : public Geo {
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36 | public:
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37 | struct Data {
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38 | int x, y, w, h;
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39 | color fgcolor;
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40 | const char* s;
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41 | } data;
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42 | constexpr Textfield (const Data& data) : data(data) {}
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43 |
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44 | virtual void draw () const override;
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45 | };
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46 |
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47 | void Circle::draw () const {
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48 | std::cout << "Circle::draw\n";
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49 | }
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50 |
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51 | void Rectangle::draw () const {
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52 | std::cout << "Rectangle::draw\n";
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53 | }
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54 |
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55 | void Textfield::draw () const {
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56 | std::cout << "Textfield::draw\n";
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57 | }
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58 |
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59 |
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60 | template <typename Base, typename... T, std::size_t... I>
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61 | constexpr std::array<Base*, sizeof...(T)> tuple_pointers (std::tuple<T...>& t, std::index_sequence<I...>) {
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62 | return {{ &std::get<I> (t) ... }};
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63 | }
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64 |
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65 | template <typename... T>
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66 | class PolymorphicContainer {
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67 | public:
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68 | constexpr PolymorphicContainer (T&&... objs)
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69 | : tuple (std::forward<T> (objs)...),
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70 | array { tuple_pointers<Geo> (tuple, std::index_sequence_for<T...> {}) } {}
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71 |
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72 | std::tuple<T...> tuple;
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73 | std::array<Geo*, sizeof...(T)> array;
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74 | };
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75 |
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76 | constexpr PolymorphicContainer MainScreen {
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77 | Circle({.x=0, .y=10, .r=20, .fgcolor=color::red, .bgcolor=color::red }),
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78 | Rectangle({.x=100, .y=10, .w=20, .h=10, .fgcolor=color::blue }),
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79 | Textfield({.x=100, .y=10, .w=20, .h=10, .fgcolor=color::black, .s="Hallo" }),
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80 | };
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81 |
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82 | template <typename F, typename... T, std::size_t... I>
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83 | void staticIteration (const std::tuple<T...>& t, F&& f, std::index_sequence<I...>) {
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84 | ((f (std::get<I> (t)), 0), ...);
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85 | }
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86 |
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87 | template <typename F, typename... T>
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88 | void staticIteration (const std::tuple<T...>& t, F&& f) {
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89 | staticIteration (t, std::forward<F> (f), std::index_sequence_for<T...> {});
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90 | }
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91 |
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92 | int main () {
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93 | for (const Geo* obj : MainScreen.array) {
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94 | obj->draw ();
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95 | }
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96 |
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97 | staticIteration (MainScreen.tuple, [&] (const auto& elem) {
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98 | elem.draw ();
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99 | });
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100 | }
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