The engineer who decided that getting time itself right was worth a fifteen-year career - and a website built to prove your calendar code is broken.
Most engineers treat time as a solved problem. A timestamp is a number, a day is 24 hours, a year is 365. Dave DeLong knows that every one of those sentences is a bug waiting to happen.
He has spent fifteen years building iOS and macOS software, and somewhere along the way the calendar became a calling. He wrote a Swift library called Time for doing calendrical arithmetic without losing your mind, and a companion site - yourcalendricalfallacyis.com - that exists for the sole purpose of telling you, gently, that your assumption about days and clocks is wrong. There are dozens of fallacies. You have probably shipped three of them.
That is the shape of the whole career: take a thing everyone thinks is boring, look closer, and find the place where it is quietly on fire. Right now he is doing it inside a stealth startup, after a run at Apple that touched almost every corner of the platform you carry in your pocket.
He's just this guy, you know?
Chocolate and peanut butter are evidence of a benevolent cosmic design.
Inside Apple, DeLong did not stay in one lane. He worked on UIKit, the framework that draws nearly every button you have ever tapped. He worked on Apple Maps. He did a stint in Developer Evangelism, the job of standing between Apple's engineers and the developers trying to use their work.
From 2013 to 2015 he led the WWDC app - the one now called Developer - that hundreds of thousands of people open every June. And when Apple lit the fuse on a new generation of technology, he was in the room: he was closely involved with the first releases of Swift, WatchKit, HomeKit, and HealthKit.
In 2020 he moved to Siri. There he became a core contributor to the conversational engine runtime and owner of several foundational frameworks. He also did something quietly radical for a large organization: he led the API Review team, the group that reads every interface Siri's engineers want to publish and asks whether it is correct, maintainable, consistent - and whether it feels good in the hands of the person who has to use it. Ergonomic fit, on the official checklist. That tells you everything about how he thinks.
A Swift library for calendrical calculations that refuses to let dates and time zones quietly corrupt your data.
Turns a plain string like "2 + 3 * 4" into a number - functions, variables, and all. 800+ stars and counting.
A whole website cataloguing the wrong things you believe about dates and clocks. Required reading before you write a scheduler.
"A Better MVC." Three words, one heresy: maybe the architecture pattern everyone copy-pastes is not the one you actually want.
On the marquee for one of the Swift community's flagship gatherings in 2019.
Recurring fixture on the continent's iOS conference stages, from Logroño to Berlin.
Talks on API design, the laws of magic, and making interfaces that respect the people who use them.
His subjects read like a confession of obsessions: API design, MVC versus MVVM, internationalization, NSOperations, and - of course - calendar and date calculations. He also teaches engineers how to give a talk in the first place, which is the kind of thing only someone who has bombed and recovered on stage knows how to do.
There is a kind of engineer whose real legacy is not a product but a paragraph - the explanation, written once, that thousands of strangers find at two in the morning when nothing else makes sense.
DeLong is that engineer. He sits in the top 0.05% of all-time contributors on Stack Overflow, user number 115730, a five-digit account from the era when the site was young. That ranking is not a vanity metric. It means that across more than a decade, his answers about Cocoa, dates, operations queues, and the strange edges of the Apple frameworks kept being the ones people upvoted, bookmarked, and quietly copied into production. Help, compounded.
He keeps writing at davedelong.com, where the posts run long and unhurried. He has published deep series on app architecture, on composable networking, on conditional compilation, and on the deceptively bottomless subject of doing date math correctly. The blog is not content marketing. It is an engineer thinking out loud, in public, at a level of patience the internet rarely rewards and he supplies anyway.
And he stays close to the language itself. DeLong is an active participant in Swift Evolution, the open process by which Swift changes - the place where a single well-argued comment can alter how millions of people will write code for years. It is the natural habitat for someone whose day job at Siri was deciding whether an API felt right. He is not a spectator to Swift. He is one of the voices in the room arguing over the commas.
Correct, maintainable, and a pleasure to use.
An active voice in the public debates that shape the language's future, one proposal at a time.
Long-form essays on architecture, networking, and the eternal war against broken date logic.
Leaving Apple after seven years is not a small thing. The frameworks, the WWDC stage, the API Review meetings - that is a place most engineers spend a career trying to reach, not leave. DeLong left to do the one thing a large company cannot offer: start over with an empty repository and decide everything himself.
The details of the stealth startup are, by definition, not public. What is public is the shape of the person walking into it: someone who has shipped to billions of devices and still cares whether a single method name reads cleanly; someone who built an entire website to argue about leap seconds; someone whose résumé tagline is "Engineer, Architect, & Mentor" with the mentor part meant sincerely. Whatever he is building, you can guess two things about it. The architecture will be argued over before a line is written. And the dates will be correct.
That is the through-line of the whole story. From Provo to UIKit to Siri to a stealth office somewhere in Utah, Dave DeLong has treated software the way a good editor treats a sentence - convinced that the difference between fine and right is worth the extra hour, and that someone, somewhere, at two in the morning, will be grateful he took it.