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POBest Practice For List of Polymorphic Objects in C++
 

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    <p>What is a common practice for the storage of a list of base class pointers each of which can describe a polymorphic derived class?</p> <p>To elaborate and in the interest of a simple example lets assume that I have a set of classes with the following goals:</p> <ol> <li>An abstract base class whose purpose is to enforce a common functionality on its derived classes.</li> <li>A set of derived classes which: can perform a common functionality, are inherently copyable (this is important), and are serializable.</li> </ol> <p>Now alongside this required functionality I want to address the following key points:</p> <ol> <li>I want the use of this system to be safe; I don't want a user to have undefined errors when he/she erroneously casts a base class pointer to the wrong derived type.</li> <li>Additionally I want as much as possible the work for copying/serializing this list to be taken care of automatically. The reason for this is, as a new derived type is added I don't want to have to search through many source files and make sure everything will be compatible.</li> </ol> <p>The following code demonstrates a simple case of this, and my proposed (again I am looking for a common well thought out method of doing this, mine may not be so good) solution.</p> <pre><code>class Shape { public: virtual void draw() const = 0; virtual void serialize(); protected: int shapeType; }; class Square : public Shape { public: void draw const; // draw code here. void serialize(); // serialization here. private: // square member variables. }; class Circle : public Shape { public: void draw const; // draw code here. void serialize(); // serialization here. private: // circle member variables. }; // The proposed solution: rather than store list&lt;shape*&gt;, store a generic shape type which // takes care of copying, saving, loading and throws errors when erroneous casting is done. class GenericShape { public: GenericShape( const Square&amp; shape ); GenericShape( const Circle&amp; shape ); ~GenericShape(); operator const Square&amp; (); // Throw error here if a circle tries to get a square! operator const Circle&amp; (); // Throw error here if a square tries to get a circle! private: Shape* copyShape( const Shape* otherShape ); Shape* m_pShape; // The internally stored pointer to a base type. }; </code></pre> <p>The above code is certainly missing some items, firstly the base class would have a single constructor requiring the type, the derived classes would internally call this during their construction. Additionally in the GenericShape class, copy/assignment constructor/operator would be present.</p> <p>Sorry for the long post, trying to explain my intents fully. On that note, and to re-iterate: above is my solution, but this likely has some serious flaws and I would be happy to hear about them, and the other solutions out there!</p> <p>Thank you</p>
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