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copied!<p>Your <code>interact()</code> functions don't have the same signature: In the derived classes they should also be</p> <pre><code>virtual void interact(Base * b); </code></pre> <p>The <code>virtual</code> is optional, of course, but for clarity I'd put it in there.</p> <p>To find out whether DerivedA::interact() should do something with it's parameter, you can implement another virtual functions in your base class:</p> <pre><code>virtual canDoX(Base * b); virtual canDoY(Base * b); </code></pre> <p>Then in the derived implementations it could look like this:</p> <pre><code>// DerivedA void interact(Base * b) { if (b->canDoX() && b->c) delete this; } // DerivedB void interact(Base * b) { if(b->canDoY()) c = true; } </code></pre> <p><strong>Update:</strong> Since you liked Frerich Raabe's answer, let me explain why I think my approach is a bit better.<br> Following his advice, one has to create an <code>interact()</code> method for each derived class in the base and all other derived classes that can interact with a certain class.<br> With my solution one would have to add methods for certain properties, that can also be combined. If you have a Troll it would return <code>true</code> in its <code>canBeKilled()</code> method. An apple canBeEaten() and a tasty wild animal <code>canBeKilled()</code> and then <code>canBeEaten()</code>.<br> If you can combine the properties, you have to add fewer functions.</p> <p>Furthermore: If the troll drank some elixir making it invulnerable for a period of time, it returns <code>canBeKilled() == false</code> and that's it. You don't have to check the <code>isInvulnerable()</code> flag in each other interacting class.</p>

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