Thanks for the write-up. My biggest fear is not references, overloads or memory management, but rather just the layout of their structures.

We have this:

    sizeof(String) == 24
    sizeof(Option<String>) == 24

Which is cool. But Option<T> is defined like this:

    enum Option<T> {
       Some(T),
       None,
    }

I didn't find any "template specialization" tricks that you would see in C++, as far as I can see the compiler figures out some trick to squeeze Option<String> into 24 bytes. Whatever those tricks are, unless rustc has an option to export the layout of a type, you will need to implement yourself.