[jtolmar]

IIRC: capnproto generates messages that you could deserialize by casting them to the right struct, but refrains from actually doing it that way. Instead it generates a bunch of accessor methods that parse the data, as if you were reading something that's not basically a c-struct, like a protobuff.

[kentonv]

That's basically correct. Cap'n Proto generates classes with inline accessor methods that do roughly the same pointer arithmetic that the compiler would generate for struct access.

There's a couple subtle differences:

* The struct is allowed to be shorter than expected, in which case fields past the end are assumed to have their schema-defined default values. This is what allows you to add new fields over time while remaining forwards- and backwards-compatible.

* Pointers are in a non-native format. They are offset-based (rather than absolute) and contain some extra type information (such as the size of the target, needed for the previous point). Following a pointer requires validating it for security.

(Disclosure: I'm the author of Cap'n Proto.)