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<p>You can use free functions to model the <code>drawable</code> aspect of your objects:</p> <pre><code>#include <iostream> class Image { }; class Sprite { }; class Model3D { }; namespace draw_aspect { void draw(Image const& image) { std::cout << "drawing image\n"; } void draw(Sprite const& sprite) { std::cout << "drawing sprite\n"; } void draw(Model3D const& model3D) { std::cout << "drawing model3D\n"; } } </code></pre> <hr> <p>Now, either use three separate vectors (this could well be most optimal, depending on the ordering relationship between the objects across collections?), or consider a variant type vector:</p> <h2>1. Using variant types</h2> <pre><code>#include <boost/variant.hpp> using SceneObject = boost::variant<Image, Sprite, Model3D>; namespace draw_aspect { struct draw_visitor : boost::static_visitor<> { template <typename T> void operator()(T const& t) const { draw(t); } }; void draw(SceneObject const& sobj) { static const draw_visitor _vis; boost::apply_visitor(_vis, sobj); } } </code></pre> <p>A complete proof of concept of the latter: <strong><a href="http://coliru.stacked-crooked.com/a/dfced2cee5b4d4b0" rel="noreferrer">Live on Coliru</a></strong></p> <pre><code>#include <vector> class SceneManager //controls everything in the "world" game { public: void Add(SceneObject v) { _worldObjects.emplace_back(std::move(v)); } friend void draw(SceneManager const& sm) { return sm.draw(); } private: void draw() const { for(auto& sobj : _worldObjects) draw_aspect::draw(sobj); } std::vector<SceneObject> _worldObjects; //the vector that contains all of them }; int main() { SceneManager sman; sman.Add(Image()); sman.Add(Sprite()); sman.Add(Model3D()); sman.Add(Image()); draw(sman); } </code></pre> <p>Outputs </p> <pre><code>drawing image drawing sprite drawing model3D drawing image </code></pre> <h2>2. Separate collections</h2> <p>The alternative using separate vectors: <strong><a href="http://coliru.stacked-crooked.com/a/09c65e2d5e184c18" rel="noreferrer">Live on Coliru</a></strong></p> <pre><code>class SceneManager //controls everything in the "world" game { public: void Add(Image v) { _images .emplace_back(std::move(v)); } void Add(Sprite v) { _sprites .emplace_back(std::move(v)); } void Add(Model3D v) { _model3Ds.emplace_back(std::move(v)); } friend void draw(SceneManager const& sm) { return sm.draw(); } private: void draw() const { for(auto& sobj : _images) draw_aspect::draw(sobj); for(auto& sobj : _sprites) draw_aspect::draw(sobj); for(auto& sobj : _model3Ds) draw_aspect::draw(sobj); } std::vector<Image> _images; std::vector<Sprite> _sprites; std::vector<Model3D> _model3Ds; }; int main() { SceneManager sman; sman.Add(Image()); sman.Add(Sprite()); sman.Add(Model3D()); sman.Add(Image()); draw(sman); } </code></pre> <p>Note that the output is <strong>different</strong> (ordering):</p> <pre><code>drawing image drawing image drawing sprite drawing model3D </code></pre>
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