StackOverflow2013

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POHow can I avoid dynamic_cast in my C++ code?
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copied!<p>Let's say I have the following class structure:</p> <pre><code>class Car; class FooCar : public Car; class BarCar : public Car; class Engine; class FooEngine : public Engine; class BarEngine : public Engine; </code></pre> <p>Let's also give a <code>Car</code> a handle to its <code>Engine</code>. A <code>FooCar</code> will be created with a <code>FooEngine*</code> and a <code>BarCar</code> will be created with a <code>BarEngine*</code>. Is there a way to arrange things so a <code>FooCar</code> object can call member functions of <code>FooEngine</code> without downcasting?</p> <p>Here's why the class structure is laid out the way it is right now:</p> <ol> <li>All <code>Car</code>s have an <code>Engine</code>. Further, a <code>FooCar</code> will only ever use a <code>FooEngine</code>.</li> <li>There are data and algorithms shared by all <code>Engine</code>s that I'd rather not copy and paste.</li> <li>I might want to write a function that requires an <code>Engine</code> to know about its <code>Car</code>.</li> </ol> <p>As soon as I typed <code>dynamic_cast</code> when writing this code, I knew I was probably doing something wrong. Is there a better way to do this?</p> <p>UPDATE:</p> <p>Based on the answers given so far, I'm leaning towards two possibilities:</p> <ol> <li>Have <code>Car</code> provide a pure virtual <code>getEngine()</code> function. That would allow <code>FooCar</code> and <code>BarCar</code> to have implementations that return the correct kind of <code>Engine</code>.</li> <li>Absorb all of the <code>Engine</code> functionality into the <code>Car</code> inheritance tree. <code>Engine</code> was broken out for maintenance reasons (to keep the <code>Engine</code> stuff in a separate place). It's a trade-off between having more small classes (small in lines of code) versus having fewer large classes.</li> </ol> <p>Is there a strong community preference for one of these solutions? Is there a third option I haven't considered?</p>

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