Doesn't C++ not have a stable ABI? Doesn't that kind of make it difficult to interop with it? The ABI is an implementation defined thing by the compiler, right?
You don’t need a stable ABI per se if you’re working with source-level interop. Also, while it doesn’t have one in theory, it does in practice on each platform if I recall correctly.
If you consider the compiler to be part of the platform, that’s mostly true.
I think the hard problem in practice is that headers and templates make for a very fuzzy boundary between library code and client code. Calling C++ from Rust already works fine for traditional OO code, but it’s hard to imagine that anything could ever use modern templated C++ code that isn’t a full superset of C++.
If I'm not mistaken you can mix'n'match shared libraries built by either compiler on Linux. I think that's also true for individual object files within the executable. Same is true for Windows. I can't recall the state on Darwin & I don't know the state of other platforms.
I don't think templated C++ code needs to be a full superset of C++. For example, cxx provides bridged implementations for CxxVector. If cxx provided an easy-to-use mechanism to define your own bridging type without a lot of boilerplate, that could open up far more interop than is possible today.
