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Since last fall, Neven has been doing an internship to develop a new aliasing model for Rust: Tree Borrows. Hang on a second, I hear you say – doesn’t Rust already have an aliasing model? Isn’t there this “Stacked Borrows” that Ralf keeps talking about? Indeed there is, but Stacked Borrows is just one proposal for a possible aliasing model – and it has its problems. The purpose of Tree Borrows is

I have been thinking about the semantics of Rust – as in, the intended behavior of Rust programs when executed, in particular those containing unsafe code – a lot. Probably too much. But all of these thoughts are just in my head, which is not very useful when someone else wants to try and figure out how some tricky bit of unsafe Rust code behaves. As part of the Unsafe Code Guidelines project, we

In my previous blog post on pointer provenance, I have shown that not thinking carefully about pointers can lead to a compiler that is internally inconsistent: programs that are intended to be well-behaved get miscompiled by a sequence of optimizations, each of which seems intuitively correct in isolation. We thus have to remove or at least restrict at least one of these optimizations. In this pos

Pointers Are Complicated II, or: We need better language specs Some time ago, I wrote a blog post about how there’s more to a pointer than meets the eye. One key point I was trying to make is that just because two pointers point to the same address, does not mean they are equal in the sense that they can be used interchangeably. This “extra information” that distinguishes different pointers to the

"What The Hardware Does" is not What Your Program Does: Uninitialized Memory This post is about uninitialized memory, but also about the semantics of highly optimized “low-level” languages in general. I will try to convince you that reasoning by “what the hardware does” is inherently flawed when talking about languages such as Rust, C or C++. These are not low-level languages. I have made this poi

This summer, I am again working on Rust full-time, and again I will work (amongst other things) on a “memory model” for Rust/MIR. However, before I can talk about the ideas I have for this year, I have to finally take the time and dispel the myth that “pointers are simple: they are just integers”. Both parts of this statement are false, at least in languages with unsafe features like Rust or C: Po

My current research project – and the main topic of my PhD thesis – is about developing a semantic model of the Rust programming language and, most importantly, its type system. Rust is an attempt of Mozilla to find a sweet spot in the design space of programming languages: A language that provides low-level resource management (making it a systems language), is convenient for programmers and guar

Welcome to Rust-101 This is Rust-101, a small tutorial for the Rust language. It is intended to be an interactive, hands-on course: I believe the only way to really learn a language is to write code in it, so you should be coding during the course. If you have any questions that are not answered here, check out the “Additional Resources” below. In particular, the IRC channel is filled with awesome