I worked in C/C++ for a long time, though it’s been a while now. I just went to look at whether Rust had any bindings for MPI. It does - rsmpi. But they’re not fully implemented, and only support a restricted subset of MPI implementations which are pretty much the latest versions. Some others might work, but it is not explicitly tested against them. Without that, there’s a whole class of distributed applications that you’d be ill advised to write in Rust using that library, because it’s such a fundamentally core library for distributed applications, which needs to be compiled differently and with specific versions to handle the specialist interconnects on HPC systems. If you only support the latest versions, your code is not very portable to other machines.