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POTransparent aggregation of classes
 

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    <p>I'm trying to embed some game classes using a scripting language. Suppose my main structure is:</p> <pre><code>class BaseGameObject { public: virtual ~BaseGameObject() { } }; class DerivedGameObject : public virtual BaseGameObject { }; </code></pre> <p>And then, I want to attach information about how I bind this class on the script engine. I want to keep the cohesion with them as minimal as possible, so I've ended with this template pattern:</p> <pre><code>class ScriptLanguageBinder { public: virtual void bind(VM* vm) = 0; }; template &lt; typename GameObject &gt; class GameObjectLanguageBinder : public GameObject, public ScriptLanguageBinder { virtual void bind(VM* vm) { vm-&gt;bind&lt;GameObject&gt;(static_cast&lt;GameObject*&gt;(this)); } }; template &lt; typename GameObject &gt; BaseGameObject* gameObjectBuilder() { return new GameObjectLanguageBinder&lt;GameObject&gt;(); } </code></pre> <p>So I have a factory that build the "wrapped" BaseGameObject and returns the GameObjectLanguageBinder in place. This way, the rest of the system uses the resulting class as a BaseGameObject*, the script language dependency is confined in a set of classes that do not harm the Game ecosystem, and only my Script engine need to know that in fact it is a GameObjectLanguageBinder. This is working very well, aside one point:</p> <p>To get back the ScriptLanguageBinder object from the BaseGameObject* I need to do this:</p> <pre><code>ScriptLanguageBinder* binder = dynamic_cast&lt;ScriptLanguageBinder*&gt;(my_game_object); </code></pre> <p>Which is undesirable as I want to squeeze all performance I can from the code execution (It's a mobile game engine, so yes, performance counts).</p> <p>So I was wondering if there is some non-obtrusive, transparent way to achieve this <strong>without</strong> using dynamic cast. I thought in using a Visitor pattern, but this pattern is a blocker when you want to extend the classes you visit, so it's a no go.</p> <p>ps: the factory is <em>ultra</em> over-simplified on this example.</p>
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    1. USscooterman
    1. USscooterman
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    1. CONote: Absolutely need a virtual destructor if you plan to delete a pointer to the base class only. Incidentially, this can serve as the one virtual function you need. :p
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    2. COYes, I know that. The classes arent these, I just simplified everything here :)
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      1. USscooterman
 

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