Surprised to read that the compiler already supports some C++ types? That’s news to me. It’s not clear to me if that’s already in the shipping compiler or in some other version or just a proposal.
The original flag was "-experimental-cxx-interop", now it is "-enable-cxx-interop"
See here for examples of it in use, including interop with the C++ std library types:
for example, I can inject variables into the C preprocessor in my build settings and have a C header that defines constant strings with those variables, which I can then import directly into Swift as a module
It's usually as simple as calling data() on a vector or std::string (as well as having a function to return the length or size of the data buffer). And if you wrap your header file in the normal C externs, it shouldn't compile if you do things that are not allowed in C, if I remember.
But you are right it can be a lot of work if you have a large surface area. I try to stick to tight, focused APIs, and data is normal C structs which work fine in C++ as well.