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POAvoiding dynamic_cast/RTTI
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copied!<p>I was recently working on a piece of C++ code for a side project (the <a href="https://sourceforge.net/projects/cpp-markdown/" rel="noreferrer"><code>cpp-markdown</code> library</a>, for the curious), and ran into a coding question that I'd like some opinions on.</p> <p><code>cpp-markdown</code> has a base class called <code>Token</code>, which has a number of subclasses. Two of the main subclasses are <code>Container</code> (which holds collections of other <code>Token</code>s) and <code>TextHolder</code> (used as a base class for <code>Token</code>s that contain text, of course).</p> <p>Most of the processing is handled via virtual functions, but some of it was better handled in a single function. For that, I ended up using <code>dynamic_cast</code> to down-cast the pointer from a <code>Token*</code> to one of its subclasses, so I could call functions that are specific to the subclass and its child classes. There's no chance the casting would fail, because the code is able to tell when such a thing is needed via virtual functions (such as <code>isUnmatchedOpenMarker</code>).</p> <p>There are two other ways I could see to handle this:</p> <ol> <li><p>Create <em>all</em> of the functions that I want to call as virtual functions of <code>Token</code>, and just leave them with an empty body for every subclass except the one(s) that need to handle them, or...</p></li> <li><p>Create a virtual function in <code>Token</code> that would return the properly-typed pointer to <code>this</code> when it's called on certain subtypes, and a null pointer if called on anything else. Basically an extension of the virtual function system I'm already using there.</p></li> </ol> <p>The second method seems better than both the existing one and the first one, to me. But I'd like to know other experienced C++ developers' views on it. Or whether I'm worrying too much about trivialities. :-)</p>

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