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POC++ Virtual Methods for Class-Specific Attributes or External Structure
 

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  1. POC++ Virtual Methods for Class-Specific Attributes or External Structure
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    <p>I have a set of classes which are all derived from a common base class. I want to use these classes polymorphically. The interface defines a set of getter methods whose return values are constant across a given derived class, but vary from one derived class to another. e.g.:</p> <pre><code>enum AVal { A_VAL_ONE, A_VAL_TWO, A_VAL_THREE }; enum BVal { B_VAL_ONE, B_VAL_TWO, B_VAL_THREE }; class Base { //... virtual AVal getAVal() const = 0; virtual BVal getBVal() const = 0; //... }; class One : public Base { //... AVal getAVal() const { return A_VAL_ONE }; BVal getBVal() const { return B_VAL_ONE }; //... }; class Two : public Base { //... AVal getAVal() const { return A_VAL_TWO }; BVal getBVal() const { return B_VAL_TWO }; //... }; </code></pre> <p>etc.</p> <p>Is this a common way of doing things? If performance is an important consideration, would I be better off pulling the attributes out into an external structure, e.g.:</p> <pre><code>struct Vals { AVal a_val; VBal b_val; }; </code></pre> <p>storing a <code>Vals*</code> in each instance, and rewriting <code>Base</code> as follows?</p> <pre><code>class Base { //... public: AVal getAVal() const { return _vals-&gt;a_val; }; BVal getBVal() const { return _vals-&gt;b_val; }; //... private: Vals* _vals; }; </code></pre> <p>Is the extra dereference essentially the same as the vtable lookup? What is the established idiom for this type of situation? Are <em>both</em> of these solutions <em>dumb?</em> Any insights are greatly appreciated</p>
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    1. USacanaday
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    1. CODesign for clarity and easy scalability. Neither method will show up on the radar of a profiler unless this is your innermost program operation.
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      1. USAmardeep AC9MF
 

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