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    <p>Hmm, I don't think I understand your problem correctly, so apologies if this answer is way off the mark, but could you not have a static member of <code>S</code>, which has a static instance of <code>ftype</code>, and return a reference to that, this way, you don't need to explicitly have an instance defined in your implementation files... i.e.</p> <pre><code>template&lt;int plugin_id, class T&gt; struct S { typedef T (*ftype)(T); static ftype&amp; instance() { static ftype _fp = T::create(); return _fp; } }; </code></pre> <p>and instead of accessing <code>S&lt;SOME_PLUGIN,double&gt;::fp</code>, you'd do <code>S&lt;SOME_PLUGIN,double&gt;::instance()</code>. To instantiate, at some point you have to call <code>S&lt;&gt;::instance()</code>. Do you need this to happen automagically as well? </p> <p>EDIT: just noticed that you have a copy constructor, for <code>ftype</code>, changed the above code.. now you have to define a factory method in <code>T</code> called <code>create()</code> to really create the instance.</p> <p>EDIT: Okay, I can't think of a clean way of doing this automatically, i.e. I don't believe there is a way to (at compile time) build a list of types, and then instantiate. However you could do it using a mix... Hopefully the example below will give you some ideas...</p> <pre><code>#include &lt;iostream&gt; #include &lt;typeinfo&gt; #include &lt;boost/fusion/include/vector.hpp&gt; #include &lt;boost/fusion/algorithm.hpp&gt; using namespace std; // This simply calls the static instantiate function struct instantiate { template &lt;typename T&gt; void operator()(T const&amp; x) const { T::instance(); } }; // Shared header, presumably all plugin developers will use this header? template&lt;int plugin_id, class T&gt; struct S { typedef T (*ftype)(T); static ftype&amp; instance() { cout &lt;&lt; "S: " &lt;&lt; typeid(S&lt;plugin_id, T&gt;).name() &lt;&lt; endl; static ftype _fp; // = T::create(); return _fp; } }; // This is an additional struct, each plugin developer will have to implement // one of these... template &lt;int plugin_id&gt; struct S_Types { // All they have to do is add the types that they will support to this vector static void instance() { boost::fusion::vector&lt; S&lt;plugin_id, double&gt;, S&lt;plugin_id, int&gt;, S&lt;plugin_id, char&gt; &gt; supported_types; boost::fusion::for_each(supported_types, instantiate()); } }; // This is a global register, so once a plugin has been developed, // add it to this list. struct S_Register { S_Register() { // Add each plugin here, you'll only have to do this when a new plugin // is created, unfortunately you have to do it manually, can't // think of a way of adding a type at compile time... boost::fusion::vector&lt; S_Types&lt;0&gt;, S_Types&lt;1&gt;, S_Types&lt;2&gt; &gt; plugins; boost::fusion::for_each(plugins, instantiate()); } }; int main(void) { // single instance of the register, defining this here, effectively // triggers calls to instanc() of all the plugins and supported types... S_Register reg; return 0; } </code></pre> <p>Basically uses a fusion vector to define all the possible instances that could exist. It will take a little bit of work from you and the developers, as I've outlined in the code... hopefully it'll give you an idea...</p>
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    1. POAutomatically Instantiating over a bunch of types in C++
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    1. CO"To instantiate, at some point you have to call S<>::instance(). Do you need this to happen automagically as well?" Yes, that is the problem.
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