Right, but my point is that then you're generating a complex FFI (which requires high level info about how "operator<<" on std::cout implements streaming and no

Right, but my point is that then you're generating a complex FFI (which requires high level info about how "operator<<" on std::cout implements streaming and not bitshifting as usual), not a simple binding. Doing that automatically and "standardly" would be quite complex. Those aren't primitive types, they're abstraction built on top of the language's typesystem, g++ is not aware of what a "stream" is in C++, nor is rustc aware of what the Read and Write traits mean.