In this blog post, the author critiques the Cap’n Proto schema language. They suggest that the schema language should prioritize the call site over the schema itself and make things easier for code generators. The author discusses the challenges with nested namespaces, anonymously named entities, unions, groups, parameters and results, identifier conventions, default field values, and inheritance. They argue that while Cap’n Proto has its advantages, the difficulties in its implementation and the resulting clumsy APIs make it necessary to be selective in what features are included. The author emphasizes the importance of leaving out unnecessary features to simplify the language.
https://zenhack.net/2019/06/25/a-critique-of-the-capnproto-schema-language.html