Are type fields pure evil?

Question

As discusses in The c++ Programming Language 3rd Edition in section 12.2.5, type fields tend to create code that is less versatile, error-prone, less intuitive, and less maintai

Answer 1

A type enum can be serialized via memcpy, a v-table can't. A similar feature is that corruption of a type enum value is easy to handle, corruption of the v-table pointer means instant badness. There's no portable way to even test a v-table pointer for validity, calling dynamic_cast or typeinfo to do RTTI checks on an invalid object is undefined behavior.

For example, one instance where I choose to use a type hierarchy with static dispatch controlled by a discriminator and not dynamic dispatch is when passing a pointer to a structure through a Windows message queue. This gives me some protection against other software that may have allocated broadcast messages from a range I'm using (it's supposed to be reserved for app-local messages, do not pass GO if you think that rule is actually respected).