session-types

Since this often matters when implementing protocols, there is research about session types and verification. Here is a Rust library for session types: https://github.com/Munksgaard/session-types I believe both have some overlap.

Hi, author of the code here. Why do I use mem::transmute? To highlight the fact that when using typestate, it's useful to understand operations that change the the value of an object as distinct from those that change the type of an object. It's also a matter of efficiency -- you don't have to generate a new struct every time you change state. You can avoid the overhead without transmute, but it's still unsafe and not easily explained: https://github.com/Munksgaard/session-types/commit/3a310d205...

As others have mentioned, and as the post itself also was updated to say, you don't need const generics to support this pattern: https://github.com/Munksgaard/session-types, http://munksgaard.me/papers/laumann-munksgaard-larsen.pdf

https://github.com/Munksgaard/rust-sessions actually goes quite far in doing this (without compiler support, just using the type system).

For anyone interested in session types, we are currently working on implementing a library for them, in Rust[0]. However, as you point out, Rusts types are affine, not linear, so we're also working on a compiler plugin for Rust that let's you track protected types and make sure they aren't dropped, letting you sort of emulate linear types[1]. Most of this is still in a pretty early state (neither actually compile at the moment), and there are some fundamental problems with the plugin (it's impossible afaik for compiler plugins to examine external crates), but someone might find it interesting. Eventually, our goal is to use these tools to solve some concurrency problems in Servo. [0] https://github.com/Munksgaard/rust-sessions [1] https://github.com/Manishearth/humpty_dumpty