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POPattern for storing multiple types of struct in a C++ std::<vector> container
 

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  1. POPattern for storing multiple types of struct in a C++ std::<vector> container
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    <p>I have a data structure which represents a train, which can be made up of many types of car, for example the train engines, a grain car, a passenger car, and so on:</p> <pre><code>struct TrainCar { // ... Color color; std::string registration_number; unsigned long destination_id; } struct PowerCar : TrainCar { // ... const RealPowerCar &amp;engine; } struct CargoCar : TrainCar { // ... const RealCargoCar &amp;cargo; bool full; } std::vector&lt;TrainCar*&gt; cars; cars.push_back(new TrainCar(...)); cars.push_back(new TrainCar(...)); cars.push_back(new CargoCar(...)); cars.push_back(new CargoCar(...)); cars.push_back(new CargoCar(...)); </code></pre> <p>An algorithm will iterate through the cars in the train, and decide how to route/shunt each car (whether to keep it in the train, move it to another point in the train, remove it from the train). This code looks like:</p> <pre><code>std::vector&lt;TrainCar*&gt;::iterator it = cars.begin(); for (; it != cars.end(); ++it) { PowerCar *pc = dynamic_cast&lt;PowerCar*&gt;(*it); CargoCar *cc = dynamic_cast&lt;CargoCar*&gt;(*it); if (pc) { // Apply some PowerCar routing specific logic here if (start_of_train) { // Add to some other data structure } else if (end_of_train &amp;&amp; previous_car_is_also_a_powercar) { // Add to some other data structure, remove from another one, check if something else... } else { // ... } } else if (cc) { // Apply some CargoCar routing specific logic here // Many business logic cases here } } </code></pre> <p>I am unsure whether this pattern (with the dynamic_casts, and chain of if statements) is the best way to process the list of simple structs of varying types. The use of dynamic_cast seems incorrect.</p> <p>One option would be to move the routing logic to the structs (so like (*it)->route(is_start_of_car, &amp;some_other_data_structure...)), however I'd like to keep the routing logic together if possible.</p> <p>Is there a better way of iterating through different types of simple struct (with no methods)?, or do I keep the dynamic_cast approach?</p>
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