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POBuild class hierarchy with overridable handler functions
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  1. POBuild class hierarchy with overridable handler functions
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    copied!<p>I'm currently trying to build a class hierarchy automatically by using C++ templates. The final result is a message handler class that provides handler functions for all possible messages, given in a typelist.</p> <p>However when inheriting from that class hierarchy and trying to implement the handler function to actually do the application code <em>for some types only</em>, C++ isn't calling the function from the base class.</p> <p>The following is a minimal and complete example what I'm trying to achieve. It doesn't compile because C++ complains about not finding an overload for <code>handle( const B&amp; )</code>.</p> <pre><code>#include &lt;iostream&gt; #include &lt;typeinfo&gt; // Typelist. struct None {}; template &lt;class H, class T = None&gt; struct Typelist { typedef H Head; typedef T Tail; }; template &lt;class TL&gt; struct Handler : public Handler&lt;typename TL::Tail&gt; { using Handler&lt;typename TL::Tail&gt;::handle; virtual void handle( const typename TL::Head&amp; obj ) { std::cout &lt;&lt; "Not handled! " &lt;&lt; typeid( typename TL::Head ).name() &lt;&lt; std::endl; } }; template &lt;&gt; struct Handler&lt;None&gt; { virtual void handle() {} }; struct A {}; struct B {}; typedef Typelist&lt;A, Typelist&lt;B&gt; &gt; MsgList; struct MyHandler : Handler&lt;MsgList&gt; { void handle( const A&amp; a ) { std::cout &lt;&lt; "A!" &lt;&lt; std::endl; } }; int main() { MyHandler handler; A a; B b; handler.handle( a ); handler.handle( b ); } </code></pre>
 

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