Range types for integers (or refinement types?)

[BryanQuigley]

It seems like a natural extension of how variables (immutable by default, mutable if specified) are defined to allow the programmer to dictate a specific range of allowed values for an integer. If I know a value is only valid between 0-1000 the sooner I declare that the better it is for catching bugs, off by one errors, and more...

I'm not sure what exact syntax would work, maybe:

let mut(0,1000) x = 0i;

x is only valid from 0-1000 inclusive.

(Apologies if this is already possible, I've been parsing the docs trying to learn Rust.)

[aochagavia]

@BryanQuigley Thanks for your comments! As this is a non-trivial change to the language, I suggest that you open a discussion on http://discuss.rust-lang.org/ and see what people think. If the idea gains traction, you could write an RFC for it.

[kmcallister]

Ada has this. It would be great in Rust, as we're going for the same niche of low-level + high-assurance.

I wonder though if we should go for a more general system, such as refinement types or pre/post-conditions. There have been a number of successes bolting these onto languages like Haskell, F#, and C#. AIUI, they manage this without heavy changes to the core language. The condition checker is a mostly-separate tool that gathers proof obligations from the source code and passes them to a SMT solver.

Basically I think this is an area where we should give researchers and other interested parties some time to experiment before we standardize something into Rust itself.

[steveklabnik]

I'm pulling a massive triage effort to get us ready for 1.0. As part of this, I'm moving stuff that's wishlist-like to the RFCs repo, as that's where major new things should get discussed/prioritized.

This issue has been moved to the RFCs repo: rust-lang/rfcs#671