Hands-On Design Patterns with C++

Dynamic type registry

So far, we have assumed that the complete list of the types is known at compile time and can be encoded in the type identifier correspondence table (implemented with a switch statement, in our example). The former requirement is unavoidable in the scope of the entire program: since every constructor call is explicit somewhere, the total list of types that can be constructed is known at compile time. However, our solution is more constrained than that—we have the list of all types that are hard-coded in the factory method. No additional derived classes can be created without also adding them to the factory. Sometimes, this restriction is not as bad as it appears—for example, the list of buildings in the game may not change ...