Today I realized a new crate called pin-cell. This crate contains a type called PinCell, which is a kind of cell that is similar to RefCell, but only can allow pinned mutable references into its interior. Right now, the crate is nightly only and no-std compatible. How is the API of PinCell different from RefCell? When you call borrow_mut on a RefCell, you get a type back that implements DerefMut, allowing you to mutate the interior value.…

There are 2 hard problems in computer science: cache invalidation, naming things, and off-by-1 errors. Naming a project, tool, or concept that you want other people to use is a very hard problem. The most important thing, of course, is that the name sounds cool. Then, significantly less important, but still quite important, is that the name convey useful information to your users. This is where things get tricky. There are tons of different kinds of cool birds and sharks and reptiles we can name our projects after, but only some of those names also convey information to our users.…

A few months ago we introduced the concept of “pinned” references - pointers which “pin” the data they refer to in a particular memory location, guaranteeing that it will never move again. These are an important building block for certain patterns that had previously been hard for Rust to handle, like self-referential structs and intrusive lists, and we’ve in the process of considering stabilizing the API. One thing has always nagged about the API we have right now though: the proliferation of different reference types that it implies.…

Recently, I wrote a little a side project to sign git commits without gpg. When I did this, I decided to use the Rust 2018 edition. I also transitioned an existing library from Rust 2015 to Rust 2018 to see how that tooling worked. I thought I’d write a blog post about my experience using the Rust 2018 preview and the state of things right now. Module changes The main thing I noticed vividly was the new experience of the module system.…

Unlike most git users, I try to sign my commits. Unfortunately, the only way to do this right now is to use PGP signatures, because that is all that git is able to integrate with. This has meant that in practice I have to use GPG if I want to sign my commits, an experience I do not relish. Last week, I wrote a program to replace GPG for that purpose.…

Last time, we introduced the idea of async methods, and talked about how they would be implemented: as a kind of anonymous associated type on the trait that declares the method, which corresponds to a different, anonymous future type for each implementation of that method. Starting this week we’re going to look at some of the implications of that. The first one we’re going to look at is object safety.…

Async/await continues to move along swimmingly. We’ve accepted an RFC describing how the async/await syntax will work in Rust, and work is underway on implementing support for it in the compiler. We’re hopeful that users will be able to start experimenting with the syntax on nightly by early July. The RFC for async/await didn’t address one important thing: async methods. It is very important for people defining libraries to be able to define traits that contain async functions, like this:…

I’m really excited to announce the culmination of much of our work over the last four months: a pair of RFCs for supporting async & await notation in Rust. This will be very impactful for Rust in the network services space. The change is proposed as two RFCs:

• RFC #2394: which adds async & await notation to the language.
• RFC #2395: which moves a part of the futures library into std to support that syntax.

These RFCs will enable basic async & await syntax support with the full range of Rust features - including borrowing across yield points. The rest of this blog post just covers the answers to some anticipated frequently asked questions; for more details see the two RFCs.

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It’s hard to believe its been almost 6 weeks since the last post I made about async/await in Rust. So much has happened that these last several weeks have flown by. We’ve made exceptionally good progress on solving the problem laid out in the first post of this series, and I want to document it all for everyone. Future and the pinning API Last month I wrote an RFC called “Standard library API for immovable types”.…

I’m planning to release a 1.0.0 version of failure on March 15. Once this happens, I don’t plan to release any further breaking changes to the failure crate (though maybe someday in the distant future). Breaking changes in 1.0 failure is in a somewhat unique position as being a significant part of the public API of other libraries that depend on it. Whether they use the Error struct or derive Fail for a custom error type, this becomes a part of the API they expose to other users.…