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    <p>I'll try to strip away the details of your model and focus on the following abstract design:</p> <pre><code> struct A struct DA : A { { }; }; //============================================================================== struct B struct DB : B { { A* p; DA* pD; // Avoid this }; }; </code></pre> <p>Now what you are trying to do is to avoid adding an <em>extra</em> member variable to <code>DB</code>, and be able to treat the pointer <code>p</code> inherited from <code>B</code> as if it were of type <code>DA*</code>.</p> <p>You can structure classes <code>B</code> and <code>DB</code> this way:</p> <pre><code>struct B { private: A* p; public: B(A* _p) : p(_p) { } A* get_p() { return p; } } struct DB : B { public: B(DA* _p) : B(_p) { } DA* get_p() { return static_cast&lt;DA*&gt;(A::get_p()); } } </code></pre> <p>Superclass <code>B</code> will hold a pointer of type <code>A*</code>. This pointer is set at construction time. If the constructor is invoked while creating an instance of <code>DB</code>, a pointer to an object of type <code>DA</code> will be stored. <code>DB</code> provides a function <code>get_p()</code> that hides <code>B</code>'s version of <code>get_p()</code> and returns a (properly casted) pointer of type <code>DA*</code>. </p> <p>Due to this design, the <code>static_cast&lt;&gt;</code> in <code>DB::get_p()</code> is guaranteed to be safe (unless you use virtual inheritance, in which case you should use the less efficient <code>dynamic_cast&lt;&gt;</code>).</p> <p>Internal operations of <code>B</code> would access the pointer <code>p</code> directly. Clients of <code>B</code> would retrieve it through a call to <code>B::get_p()</code>. Inside of <code>DB</code>, and for clients of <code>DB</code> as well, you would access the object pointed to by <code>p</code> by retrieving the pointer through function <code>B::get_p()</code>, rather than directly dereferencing <code>p</code>.</p>
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    1. POWhen superclass holds pointer to X, and subclass to Y : X
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    1. USAndy Prowl
    1. USAndy Prowl
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    1. POWhen superclass holds pointer to X, and subclass to Y : X
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    1. COShouldn't `B(DA* _p) : p(_p) { }` be `DB(DA* _p) : B(_p) { } ` instead?
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      1. USRemy Lebeau
    2. CO@RemyLebeau: Of course. Fixed, thank you!
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    3. COSo basically every time in DA I'd need access to DB*, extra function call invoking a static/dynamic cast is needed. Is there a way to do this, avoiding the cast? Maybe if we declare a union of A* and DA* for p, instead of just A*?
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      1. USgt6989b
 

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