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POPolicy vs polymorphic speed
 

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    <p>I read that using a policy class for a function that will be called in a tight loop is much faster than using a polymorphic function. However, I setup this demo and the timing indicates that it is exactly the opposite!? The policy version takes between 2-3x longer than the polymorphic version.</p> <pre><code>#include &lt;iostream&gt; #include &lt;boost/timer.hpp&gt; // Policy version template &lt; typename operation_policy&gt; class DoOperationPolicy : public operation_policy { using operation_policy::Operation; public: void Run(const float a, const float b) { Operation(a,b); } }; class OperationPolicy_Add { protected: float Operation(const float a, const float b) { return a + b; } }; // Polymorphic version class DoOperation { public: virtual float Run(const float a, const float b)= 0; }; class OperationAdd : public DoOperation { public: float Run(const float a, const float b) { return a + b; } }; int main() { boost::timer timer; unsigned int numberOfIterations = 1e7; DoOperationPolicy&lt;OperationPolicy_Add&gt; policy_operation; for(unsigned int i = 0; i &lt; numberOfIterations; ++i) { policy_operation.Run(1,2); } std::cout &lt;&lt; timer.elapsed() &lt;&lt; " seconds." &lt;&lt; std::endl; timer.restart(); DoOperation* polymorphic_operation = new OperationAdd; for(unsigned int i = 0; i &lt; numberOfIterations; ++i) { polymorphic_operation-&gt;Run(1,2); } std::cout &lt;&lt; timer.elapsed() &lt;&lt; " seconds." &lt;&lt; std::endl; } </code></pre> <p>Is there something wrong with the demo? Or is just incorrect that the policy should be faster?</p>
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    1. USDavid Doria
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    1. COIt depends on your optimisation settings. Show us how your compiler is being invoked, and tell us what compiler it is.
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    2. COVisual C++ 2010 optimizes the policy_operation loop away, your benchmark is off...
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    3. COg++ optimizes away the policy loop as well.
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