Template class for type-based function dispatch.

This class allows registering function pointers associated with specific derived types of a base class. When invoked with a base class reference, it will look up and call the appropriate registered function.

When no registered type matches the object, the call throws std::runtime_error (the historical behavior) unless a fall-through handler has been installed via registerDefault, in which case that handler is invoked instead and the dispatcher can degrade gracefully.

Template Parameters

base_t	The base class type that will be the first parameter
signature_t	The function signature (e.g., return_t(Args...))