[flatline]

Interfaces! Inheritance! Looks promising. Protocol buffers are nice for their compact encoding and multi-language generator support but as a schema language they are really cumbersome. Composition is pretty much all you get, there are no longer required fields, you can't even use enums as a key type in a map. I'm sure their use cases are not necessarily the same as mine but sometimes I miss just using plain old XML.

[kentonv]

To be clear, Cap'n Proto's serialization layer, from a schema perspective, is almost exactly the same as Protobuf (though with a very different underlying encoding).

The interfaces and inheritance relate to the RPC system. The interfaces are for remote objects.

See: https://capnproto.org/rpc.html