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    <p>There are two axises of variation in writing: the write0/write1 choice and the MsgA/B/C.... choice. </p> <p>Conceptually that means you need NxM implementations of a <code>write</code> function. Of course, if a write implementation is added, or a message type is added, this leads to resp. M or N extra functions to be added. </p> <p>For both axises you can choose whether to implement them using static or dynamic polymorphism. The static polymorphism can be done using templates or using function overrides.</p> <p>It could be done by creating a N element class hierarchy with M write functions in each class. But it would soon become a maintenance nightmare. Unless the message content is also runtime polymorphic. But the question is about static polymorphism for the messages.</p> <p>Since runtime polymorphism is ruled out because of too elaborate (and you can't have a template function virtual, which would decrease the verbosity of overrides), we need to implement a little type-dispatching routine, converting runtime information into compile-time information.</p> <p>More specifically: templatize the main action (in the example called <code>Tmain</code>) with the writer-to-use, and call it with the right template argument from the 'real' <code>main</code>.</p> <p>This omits the use of a 'global' choice variable, yet is object-oriented and concise.</p> <pre><code> // twodimensionalpolymorph.cpp // #include &lt;iostream&gt; using namespace std; class Write0 { public: template&lt; typename tMsg &gt; void operator()( /*const*/ tMsg&amp; msg ) { cout &lt;&lt; "write0: " &lt;&lt; msg.name() &lt;&lt; endl; }; }; class Write1 { public: template&lt; typename tMsg &gt; void operator()( /*const*/ tMsg&amp; msg ) { cout &lt;&lt; "write1: "&lt;&lt; msg.name() &lt;&lt; endl; }; }; struct MsgA { const char *name() { return "MsgA"; } }; struct MsgB { const char *name() { return "MsgB"; } }; struct MsgC { const char *name() { return "MsgC"; } }; struct MsgD { const char *name() { return "MsgD"; } }; // the Tmain does the real action // template&lt; typename Writer &gt; int Tmain( Writer&amp; write, int argc, char** args ) { write( MsgA() ); write( MsgB() ); write( MsgB() ); write( MsgD() ); return 0; } // the main merely chooses the writer to use // int main( int argc, char** args ) { if( argc==1 ) return Tmain( Write0(), argc, args); else return Tmain( Write1(), argc, args); } </code></pre>
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    1. POHow else to achieve "templated function pointers"?
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    1. CONothing was ruled out for being "too elaborate;" templated virtuals are simply not valid C++. Your approach is interesting and would work for some cases, but I'm calling write() from all over the program, and would like to avoid propagating the template parameter everywhere.
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    2. COBTW, minor bug in your code: you can't have rvalue refs (yet).
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    3. COI didn't state it correctly: if you want two 'dimensions' of variation (i.e. the write type and the message type) without templates, you end up with NxM implementations. That's elaborate, but would do the trick: capture function pointers, and be flexible at run time.
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