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POSpecial interaction between derived objects (i.e. mutiple dispatch)
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copied!<p>So, I have a list of base class pointers:</p> <pre><code>list<Base*> stuff; </code></pre> <p>Then, at some point one of the objects will look through all other objects.</p> <pre><code>Base * obj = ...; // A pointer from the 'stuff'-list. for (list<Base*>::iterator it = stuff.begin(); it != stuff.end(); it++) { if (obj == *it) continue; // Problem scenario is here obj->interact(it); } </code></pre> <p>What I want to achieve is that depending on what derived type<code>obj</code> and <code>*it</code> are, they will interact differently with each other, i.e. <code>DerivedA</code> will destroy itself if it's interacting with <code>DerivedB</code>, but only if <code>DerivedB</code> has set the property <code>bool c = true;</code>. So something like:</p> <pre><code>struct Base { virtual void interact(Base * b); // is always called }; struct DerivedA : public Base { virtual void interact(Base * b){} // is never called virtual void interact(DerivedB * b) // is never called { if (b->c) delete this; } }; struct DerivedB : public Base { bool c = false; virtual void interact(Base * b){} // is never called virtual void interact(DerivedA * a) // is never called { c = true; } }; // and many many more Derived classes with many many more specific behaviors. </code></pre> <p>At compile time, they are both <code>Base</code>-pointers and will not be able to call each other and expect the type to magically appear. If this was a one way relation, i.e. I knew what type of one of them, I could use the <a href="http://en.wikipedia.org/wiki/Visitor_pattern" rel="nofollow noreferrer">Visitor pattern</a>. I believe I should use some kind of <a href="http://en.wikipedia.org/wiki/Mediator_pattern" rel="nofollow noreferrer">Mediator pattern</a> but can't really figure out how since the mediator too will hold <code>Base</code>-pointers and thus it won't make a difference.</p> <p>I haven't got a clue on how to continue... anyone?</p> <hr> <p><strong>Background:</strong></p> <p>I'm creating a game, this problem originates from the <code>Room</code> class who keeps track of it's contents, i.e. what <code>GameObject</code>s are currently in the room. </p> <p>Sometimes, an object moves (for example, the player). The room will then loop over all objects that are on the soon-to-be-moved-upon floor tile (the loop above) and will check if the objects will interact with eachother. </p> <p>For example, if it's a <code>Troll</code> the <code>Player</code> would want to hurt it. Or he would just like to hurt any <code>Character</code> (both <code>Troll</code> and <code>Player</code> are derived from <code>Character</code>) that originates from any another "team" (which can be accessed from the function <code>getAlignment()</code>, which all <code>Characters</code> implement).</p>

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