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POC++ generic object factory by string name
 

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    <p>I need a way to instantiate objects based on its class name passed by as a std::string. This is working right now, but need to be generalized:</p> <pre><code>void* create(std::string name) { if(name == "classOne") return new ClassOne(); else if(name == "classTwo") return new ClassTwo(); /* ... */ } </code></pre> <p><strong>What i do not have</strong>:</p> <ul> <li>Control over the classes to be instantiated: could be thirty party classes. No changes may be done to this classes (i.e. base ancestor, polymorphic creator method, etc...)</li> <li>Full class name listing: more classes could be added later and should not incur in changes to this factory.</li> <li>Wrappers around the classes to be instantiated: As a result of the previous two points.</li> </ul> <p>Anything else is a go.</p> <p>The best use case scenario will be:</p> <pre><code>int main() { void *obj = create("classTree"); // create object based on the string name /* ... */ // once we know by context which specific class we are dealing with ClassTree *ct = (ClassTree*)obj; // cast to appropiate class std::cout &lt;&lt; ct-&gt;getSomeText() &lt;&lt; std::endl; // use object } </code></pre> <p>As a side, and maybe irrelevant note, take in account the object to be instantiated may come from a class or a struct.</p> <p><strong>ADDED INFORMATION</strong></p> <p>I see more context is needed. Here is my particular use case, simplified:</p> <pre><code>// registration mechanism int main() { std::map&lt; std::string, void(*func)(std::string, void*) &gt; processors; // map of processors by class name processors["ClassFour"] = (void(*)(std::string, void*)) &amp;classFourMessageProcessor; // register processor (cast needed from specific to generic) } // function receiving string messages void externalMessageHandler(std::string msg) { std::string objType = extractTypeFromMessageHeader(msg); // extract type from message // now that we know what we are dealing with, create the specific object void *obj = create(objType); // &lt;&lt; creator needed processors[objType](msg, obj); // dispatch message to process } // previously registered message processor void classFourMessageProcessor(std::String msg, ClassFour *obj) { std::string streetAddress = msg.substr(10, 15); // knowing the kind of message we can extract information obj-&gt;moveTheEtherTo(streetAddress); // use the created object } </code></pre> <p><strong>ADDED INFORMATION</strong></p> <p>I am using C++11 with the latest GNU compiler.</p>
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    1. COy not just instantiate the right class "once we know which specific class we are dealing with" and do the stuff you would be doing with that `void*` afterwards?
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    2. CO@Kal You might need to use `obj` before knowing what class it is.
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    3. COThis is not the normal way of creating a factory. It will not scale well due to the large if statement block. See http://stackoverflow.com/questions/5120768/how-to-implement-the-factory-pattern-in-c-correctly
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