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POC++ Only Allow a member variable to be set once
 

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    <p>It's been a while since I've jumped into C++ but I want to make sure I'm sticking to best practices when I do, including being const-correct.</p> <p>I'm currently building a library of code for a game framework and I have the following classes (summarised for simplicity):</p> <pre><code>class Screen { public: Clear(); } </code></pre> <p>and</p> <pre><code>class Game { private: Screen* screen; protected: const Screen* GetScreen() const; } </code></pre> <p>I've omitted the rest for brevity but suffice it to say, the <code>Game</code> class is responsible for the creation of the <code>Screen</code> class instance. After it is created, it should only be accessed through the <code>GetScreen()</code> method.</p> <p>The idea is, that when creating a new game, I would inherit from this base class, so as an example, during a render loop I would want to clear the screen to redraw the next frame. Now, in my above definitions, the <code>Clear()</code> method is not allowed to be called when using the <code>GetScreen()</code> method because it is not <code>const</code>. The clear method would actually change the internal workings of the class (by virtue of the fact that the previously displayed image is cleared) so that is why I left the <code>const</code> declaration out of the definition. If I made it <code>const</code> then I would have to have some of the inner workings of the <code>Screen</code> class as <code>mutable</code> but from what I've read, this would not be very const-correct.</p> <p>So, I have two parts to my question. Should I change <code>void Clear()</code> to <code>void Clear() const</code> and make parts of the inner workings <code>mutable</code>?</p> <p>Or is the an alternative that would allow me to make the <code>screen</code> member of the <code>Game</code> class only settable once by the <code>Game</code> class so that I can access the non-const member functions during the rest of the program's run time.</p> <p>Thanks for any help.</p>
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    1. COIt looks like you want `screen` to be a `Screen&` or `Screen* const` instead of `const Screen*`.
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