[0815test]

Rust developers have actually been very cautious about integrating the 'usual' sorts of PL-theory driven features in Rust. The PL theory of Rust-like languages is still in its infancy in many ways, but it has already usefully informed the design of library features like e.g. Pin<>, as well as eased the understanding of seemingly ad-hoc language features like so-called 'internal' mutability, which - as it turns out - can be described via a remarkably simple theoretical basis.