Any time I use an AI tool for something I’m deeply familiar with, I find a continual stream of mistakes and inconsistencies. When I use it on a topic I don’t know… everything sounds plausible and I don’t find mistakes. The difference worries me, and sounds a lot like the Gell-Mann Amnesia effect. AI...

I spend a lot of time reviewing code, and I think it’d be easier if I saw more tastefully broken commits. Commits construct a story about a change: “first this happened, then that, that another thing” is a good narrative; “first everything happened, the end”… not so much. Sometimes, telling that sto...

SQL databases support multi-column indices, where a single index can incorporate data from multiple columns. These are powerful, but the order of the columns matters, with differences observable in practice: there can be orders of magnitude between two similar & simple queries, depending on which us...

When I use an AI coding agent to make a plan, I make a habit of opening that plan in my editor and then leaving inline comments with questions, requests and corrections directly in the file. The agent seems to be happy enough to work with these, and I find it gives better results than reading the pl...

The Magit package for Emacs is my Git UI of choice, and git worktrees are very convenient. They mesh up particularly well by adding the built-in magit-insert-worktrees to magit-status-sections-hook. With this, the magit status buffer shows a summary of the branch/HEAD/path of all worktrees, and allo...

The TypeScript compiler options strictNullChecks and noImplicitAny interact in a strange way: enabling just strictNullChecks leads to type errors that disappear after enabling noImplicitAny too, meaning getting stricter has fewer errors! This is a low-consequence curiosity, but I did trip over it in...

I occasionally add context instructions to an AI tool, but then am not sure whether those changes were picked up by the tool. The fun way to debug this is to add “Always speak like a pirate” to the instructions. This works in all tools. Context engineering! Context I use LLM tools like Claude Code. ...

I’ve noticed different people seem to use the word “deprecating” to mean two different things, when it comes to code and/or features: either removing entirely, or discouraging its use. I think it’s useful to have specific labels for both of these of concepts, so that communication is clearer. When y...

The network tab of a browser’s developer tools shows a list of requests. Sometimes there’s a problem with one of those requests! Maybe the server is crashing and returning a 500 error, or maybe there’s an unexpected 403 permission error. The dev tools UIs provide one-click “Copy as cURL” functionali...

Hitting a bug is no fun: maybe it interferes with your work or play, or maybe it means you have to dive down a debugging rabbit hole. Remotely debugging a bug someone else has found is even less fun… I’ve settled on using a shell script for sharing executable self-contained reproducers for issues I ...

Rust’s match statement can do a lot of things, even C-style fallthough to the next branch, despite having no real support for it. It turns out to be a “shallow” feature, where the C to Rust translation is easily done, without needing to understand the code itself. The hardest part is coming to terms...

The conventional units for expressing the mileage of an electric vehicle, like Wh/km (“watt-hours per kilometer”), are dimensionally equivalent to force, N (“newtons”). It seems this has a useful physical interpretation, and we can do some rough predictive calculations by estimating the drag and rol...

Shell scripts sometimes have to append data to a file. Redirecting output with >> is the conventional way and works fine, but using tee -a instead is a usually better default, especially in continuous integration. It’s just as easy and gives automatic introspection: the same value is printed to stdo...

Memory mapping a file for reading sounds nice: turn inconvenient read calls and manual buffering into just simple indexing of a memory… but it does blocking IO under the hood, turn a &[u8] byte arrays into an async hazard and making “concurrent” async code actually run sequentially! Code affected li...

GitHub offers permalinks to versions of files and lines, within a repository. They’re easy to create (y keyboard shortcut) and have some nifty affordances like displaying a preview, plus they don’t become invalid as code changes. Use them! The permalinks use the commit hash of a particular version o...

Encoding data in decimal requires many more characters than the same data encoded in base64—06513249 vs YWJj—but using decimal is better when stored in a QR code. The magic of QR modes means all those extra digits are stored efficiently, almost as though there was no encoding at all. Decimal encodin...

Governments here in Australia have been telling us to keep distance from each other. Surprisingly, the same government has simultaneously put out posters that required people to get close, unnecessarily. They contain QR codes for contact-tracing check-ins that are small and dense, meaning they’re ha...

Error correction sounds good. It means fewer errors, right? When it comes to QR codes, that’ll mean easier scanning for people, surely? It seems like that’s not the whole story. I wondered about this, and couldn’t find an answer, so I did some exploration, and found there’s two factors in tension: t...

Taking shortcuts? Leaving edge-cases unconsidered and unhandled? Is this engineering?! My approach to programming and software engineering has been shaped by years of building open source compilers and libraries, where those edge cases matter, reliability is crucial and flexibility is important. It’...

It’s glorious to work on one task at a time, to be able to take it from start to finish completely, and then move onto the next one. Sounds great, but reality is messier than that and context switches are common. Doing so can be annoying and inefficient, but not switching means tasks and colleagues ...

The primitive integer types supported by CPUs are finite approximations to the infinite set of integers we’re all used to. This approximation breaks down and some computations will give results that don’t match real integers, like 255_u8 + 1 == 0. Often, this mismatch is something the programmer did...

Memory unsafety and memory leaks are arguably the two categories of bugs that have received the most attention for prevention and mitigation. As their names suggest, they are in the same part of “bug space”, however they are in some ways diametric opposites, and solving one does not solve the other....

Imagine being able to step forward and backwards as code runs in your debugger. Imagine being able to do an test run multiple times with exactly the same sequence of instructions and values, right down to memory addresses and IO. Imagine being able to run an executable thousands of times and then do...

I recently released version 0.3 of my simple_parallel crate, which builds on Aaron Turon’s crossbeam to resolve the stability and safety difficulties: the crate now works with Rust 1.3.0 stable, and offers safe data-parallel for loops and maps. I still don’t recommend it for general use, but I think...

A new scheme for SIMD in Rust is available in the latest nightly compilers, fresh off the builders (get it while it’s hot!). For the last two months, I’ve been interning at Mozilla Research, working on improving the state of SIMD parallelism in Rust: exposing more CPU instructions in the compiler, a...

I’m currently in San Francisco doing an internship at Mozilla Research, working on creating functionality for SIMD in the Rust programming language. (This post is designed to describe what I’m doing for people not necessarily familiar with programming or SIMD.) What is SIMD? SIMD stands for “Single ...

I just pushed travis-cargo version 0.1.3, which adds a --no-sudo command to the coveralls and coverage subcommands to allow recording/uploading test coverage without needing sudo. This is based0 on @seanmonstar’s investigation/implementation of sudo-less kcov. It works because Travis’s apt addon has...

Over the past few weeks I’ve been working on improving my slow_primes library, culminating in needing rename and the 0.2 release of primal, a Rust crate for computing properties of prime numbers with state-of-the-art algorithms, while still maintaining an idiomatic and easy-to-use interface. primal ...

Rust has some powerful tricks to model properties of aggregate types via unsafe traits with default and negative implementations. These features motivated by offering flexible concurrency/parallelism, and allow powerful closure-based APIs without losing any thread-safety (or memory-safety) guarantee...

Rust 1.0 was made with0… .number { text-align: right; } table { max-width: 600px; border-spacing: 0 0.4em; border-collapse: separate; } td { vertical-align: top; } 1stable release 2‘Rust’ compilers 3bots on Github 4years of bootstrapping (7b95b5c is the innocuous commit of the first snapshot) 5years...