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POC++: Design, Function template overriding and lack of polymorphism
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  1. POC++: Design, Function template overriding and lack of polymorphism
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    copied!<p>Have a base class A, and a derived class B which overrides function template Func:</p> <pre><code>class A { A() {...}; ~A() {}; template &lt;class T&gt; void Func(const String &amp;sInput, T &amp;tResult) {...} }; class B : public A { B() {...} ~B() {}; template &lt;class T&gt; void Func(const String &amp;sInput, T &amp;tResult) {...} }; </code></pre> <p>(Note that Func is non-virtual, given the lack of support in C++ for templated virtual functions.)</p> <p>Now have a mainprog API, class M:</p> <pre><code>class M { M(boost::shared_ptr&lt;A&gt; &amp;pInterfaceInput): pInterface(pInterfaceInput) {} template &lt;class T&gt; Evaluate(const String &amp;sInput, T &amp;tResult) { pInterface-&gt;Func&lt;T&gt;(sInput, tResult); } private: const boost::shared_ptr&lt;A&gt; pInterface; }; </code></pre> <p>I want the function Evaluate here to support calls to functions on base class A or any of its derived classes (such as B). This class was written with polymorphism in mind before I re-designed class A and B to have templated functions.</p> <p>Now the problem here is that if I pass a shared pointer of the base type to the derived type then Func of the base class will be called, not the derived class being pointed to.</p> <p>How do I get around the lack of dynamic polymorphism here? I've considered making class M a class template on the shared pointer type and having a static_cast in the constructor to ensure this type is of the base class type (A) or of a derived class.</p> <p>What's the nicest way to do this? I'd prefer not to modify classes A and B to get around this problem but all suggestions are welcome.</p> <p>Thanks.</p>
 

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