Express type inheritance and generic type parameters in generated Typescript code

[rsek]

Internally, the JSON schema (which is the source of truth for all typings) is composed in ways that parallel common OOP patterns like class inheritance and generic type parameters.

This information could be attached as a symbol property during TypeBox composition. Ideally, it will be expressed in a language-agnostic way; for the time being it would just be used for TS types, but it may be useful for Python, too (see #62).