The C++ interface is intentionally minimal: it provides only a
couple of niceties in order to largely stay out of the way. It is
mostly used to provide:
* RAII for opaque resources
* Safe up and down casting for nodes
* string_view for various resources
* Iteration over resource lists
Note that if consumers want to use it, they must be on C++17 at
minimum.
https://github.com/ruby/prism/commit/57b8dbe0e9
