actually this is likely just as performant as the "Ugly but fast" code from the famous talk. After all, this is just branching on GetType() == typeof(Dog) which is presumably boiling down to an integer comparison. This roughly the same as the following C code:
void speak_generic(void* animal, int type_id) {
if (type_id == DOG) {
dog_speak((Dog*)animal);
} else {
dispatch_speak_vtable(animal);
}
}
Advantage 2: You still get the flexibility of the vtable if you need it (for the case the type is chosen at runtime at not known). But for 90% of cases, its just as fast as the ugly C code.
Disadvantage 1: Losing a smug sense of superiority because you eschew abstractions and prefer writing verbose error-prone switch statements over clean easy to understand code.
Disadvantage 2: Writing performant code can no longer be gate kept behind archaic practices, now everyone can just use `var animal = new Dog()` and be done with it.