Here’s the thing I don’t get about module partitions: They only seem to allow one level of encapsulation.

    Program
    - Module
      - Module Partition

whereas in module systems that support module visibility, like Rust’s, you can decompose your program at multiple abstraction levels:

    Program
    - Private Module
      - Private Module
        - Private Module
        - Public Module
      - Public Module

Maybe I am missing something. It seems like you will have to rely on discipline and documentation to enforce clean code layering in C++.