This is one of my fave diagrams I've ever made on Rust. It's a simplified model of different "modes" of Rust you can program in.

Const rust is working on carving out a subset of "base" rust. Async rust is working on carving out a superset of that same base.

You could draw a similar graph including "unsafe Rust". Just like async rust, it's a superset of "base Rust", providing access to:
- raw pointer manipulation
- `extern C` to perform FFI
- `UnsafeCell` for interior mutability

The reason why this is a simplification is because even though `const` and `async` are mutually exclusive today there's nothing inherently making them incompatible (other than it not being very useful).

Also once you consider different supersets, you'll realize they may overlap.

A real challenge in language design is though to make all these different modes you can be writing Rust in still feel like they're part of the same coherent language. The goal is to provide top-notch ergonomics, performance, diagnostics, correctness, etc. for *all* modes of Rust.